the development and use of a double beam photoelectric

Western Michigan University Western Michigan University

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Master's Theses Graduate College

8-1967

The Development and Use of a Double Beam Photoelectric The Development and Use of a Double Beam Photoelectric

Polarimeter for the Study of the Faraday Effect Polarimeter for the Study of the Faraday Effect

John Norman Rowe

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Recommended Citation Recommended Citation Rowe, John Norman, "The Development and Use of a Double Beam Photoelectric Polarimeter for the Study of the Faraday Effect" (1967). Master's Theses. 3287. https://scholarworks.wmich.edu/masters_theses/3287

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THE DEVELOPMENT AND USE OF A DOUBLE BEAM PHOTOELECTRIC POLAfilMETER

FOR THE STUDY OF THE FARADAY EFFECT

Ly

J o h n N.° Rowe

A T h e s is S u b m itte d to th e

F a c u l ty o f th e S ch o o l o f G rad u a te S tu d ie s i n p a r t i a l f u l f i l l m e n t

o f th eD egree o f M a s te r o f A r ts

W este rn M ic h ig a n U n iv e r s i ty KrJLamazoo, M ich ig an

A u g u s t, 1967

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

ACKNOWLEDGEMENTS

I -wish, to acknow ledge th e v e ry h e lp f u l a d v ic e and c r i t i c i s m

g iv e n hy P r o f e s s o r S ta n le y K . D erby th ro u g h o u t th e c o u rs e o f t h i s

p r o j e c t . My th a n k s a r e e x te n d e d a ls o th e th e o th e r members o f th e

P h y s ic s D ep a rtm en t f o r t h e i r p a t i e n c e and c o o p e r a t io n . I , o f

c o u r s e , r e t a i n f u l l r e s p o n s i b i l i t y f o r t h e work p r e s e n te d h e r e .

I w ould e s p e c i a l l y l i k e t o th a n k M iss P a u la P e c k f o r h e r

c o n s ta n t en cou ragem en t and f o r ty p in g th e m a n u s c r ip t .

J o h n N. Rowe


| M A STER'S THESIS M -1304II ROW E, Jo h n N orm anI TH E DEVELO PM ENT AND USE O F A DOUBLE BEAMI PH O TO ELEC TR IC PO LA R IM ETER FOR TH E STUDYI O F TH E FARADAY E F F E C T .I| W e s te rn M ichigan U n iv e rs ity , M .A ., 1967| P h y s ic s , g e n e ra l

I| University Microfilms, Inc., Ann Arbor, Michigan£t.

R eproduced with permission of the copyright owner. Further reproduction prohibited without permission.

TABLE OP CONTENTS

CHAPTER PAGE

I GENERAL INTRODUCTION...................... . ...................................... 1

P r o p e r t i e s ............................. .......................................... . . . . 2

A p p l i c a t io n s ............................................................. 4

I I THEORY................................................................................................. 6

Zeeman E f f e c t ....................................................... 7

Q u a l i t a t i v e D e te rm in a t io n o f R o t a t i o n s 8

E x p e r im e n ta l E v id e n c e .................................... 11

S e l e c t i o n o f Compounds................... 12

I I I EXPERIMENTAL METHODS...*.............................. 14

N o n - E le c t ro n ic M e th o d s ..................................................... 14

E l e c t r o n i c M e t h o d s . . . . ..................................................... 18

IV DESIGN CONSIDERATIONS.............................................................. 22

V INSTRUMENTAL DETAILS...................... 29

L ig h t S o u rc e ................................................................. 29

M o n o ch ro m ato rs ..................... 32

p o l a r i m e te r and C e l l s .......... * ............... 34

M agnet and Pow er S u p p ly ................... . . . * . * ................. 36

E l e c t r o n i c s ............................... 37

M is c e l la n e o u s O p t ic a l C om ponents............................. 39

VI INSTRUMENT PERFORMANCE .................... 40

V II DATA............................................................. 48

P o ta s s iu m I o d id e .................................................. 49

C u p ric S u l f a t e , ........................ 49

i i


TABLE OP CONTENTS ( C o n t i n u e d )

CHAPTER PAGEF e r r i c C h lo r id e ................................................................. 52

N ic k e l S u l f a t e .................................................... 52

V I I I SUMMARY AND CONCLUSIONS................ . . . ................................. 52

I n s t r u m e n t . . , . . . . - • • 56

M easurem en ts . 57

REFERENCES .................... 59

APPENDIX.. .................................................................... 61

A S ch em atic D i a g r a m s . . . . . . . . . . . . . . . . . . . . . . . . . 62

B A lignm en t P r o c e d u r e .............................................. 67


LIST'OF FIGURES

FIGURE PAGE

1 A Type I S p ec tru m .......................................... ................................... 9

2 A Type I I S p ec tru m .......................... . ........................... ................ 9

3 ' ' L i s t o f I r o n Group I o n s . . . . . . . . . . . . . . . 13

4 A M ethod o f S tu d y in g th e F a rad a y E f f e c t .......................... 16

5 F i e ld View i n a H a lf-S h a d e A n a ly z e r .................................. 16

6 Use o f a S a v a r t P l a t e . . . . . . . . . . ............... 16

7 B lock D iagram o f P ro p o se d I n s t r u m e n t ................................. 21

8 B lock D iagram o f I n s t r u m e n t a s C o n s t r u c t e d . . . . . . . . 30

9 Equipm ent P h o to g ra p h s ..................................................................... 31

10 L ig h t S o u rce S p e c t r a . ...................... 33

11 M onochrom ator S p e c t r a . ................................................... 35

12 P h o to m u l t i p l i e r O u tp u t S ig n a l .............................. 38

13 A m p lif ie r O u tp u t . .................... 41

14 R o ta t io n V e rsu s M agnet C u r r e n t . . . ....................... 44

15 F a rad a y R o ta t io n o f W a te r .................... 46

16 L og-l;og P l o t o f th e F a ra d a y R o ta t io n o f W a t e r . . . . . 47

17 F a ra d a y R o ta t io n o f P o ta ss iu m I o d i d e .............. ...... 50

18 F a ra d a y R o ta t io n o f Copper S u l f a t e ................... .................. 51

19 F a rad a y R o ta t io n o f N ic k e l S u l f a t e . , . . . ...... 54

20 F a ra d a y R o ta t io n o f H y d ra te d N ic k e l S u l f a t e , OneP e r c e n t S o l u t i o n . . ..................... 55

21 F a ra d a y R o ta t io n o f H y d ra te d N ic k e l S u l f a t e , TenP e r c e n t S o l u t i o n . . ............................ 55

i v


L IS T OF FIGURES ( C o n t i n u e d )

FIGURE PAGB22 B lo c k D iagram o f L ig h t S o u rc e .................................... 62

23 I n p u t S ta g e s o f Tuned A m p l i f ie r ................................. 63

24 O u tp u t S ta g e s o f Tuned A m p l if ie r ............................................. 64

25 Tuned A m p lif ie r Pow er S u p p ly ...................................... 65

26 P h o to m u l t i p l i e r Pow er S u p p ly .............................................. 66


CHAPTER I

INTRODUCTION

l a 1846 K . F a rad a y * d is c o v e r e d t h a t th e p la n e o f p o l a r i z a t i o n

i s r o t a t e d when p o l a r i z e d l i g h t i s t r a n s m i t t e d th ro u g h a medium

p la c e d i n a m a g n e tic f i e l d . He d e te rm in e d t h a t t h e r o t a t i o n i s

d i r e c t l y p r o p o r t i o n a l t o t h e a p p l ie d m a g n e tic f i e l d s t r e n g t h and

th e sam p le p a th l e n g t h , and i s i n v e r s e ly r e l a t e d t o th e a n g le b e

tw een th e l i g h t r a y and t h e m a g n e tic f i e l d .

The F a ra d a y e f f e c t i s one o f a num ber o f m a g n e to o p tic e f f e c t s

d is c o v e r e d d u r in g th e l a t e 1 9 th and e a r l y 2 0 th c e n t u r i e s . Among

t h e o t h e r e f f e c t s a r e t h e Zeeman e f f e c t ( th e : s p l i t t i n g o f t h e

s p e c t r a l l i n e s p ro d u ced by a l i g h t s o u rc e p la c e d i n a m a g n e tic

f i e l d ) , t h e C o tto n -M o u to n e f f e c t ( t h e d o u b le r e f r a c t i o n e v id e n c e d

by l i q u i d s and g a s e e s p la c e d i n a m a g n e tic f i e l d ) ,, and th e K e r r

m a g n e to o p tic e f f e c t ( t h e e i l i p i t i c a l p o l a r i z a t i o n o f p la n e p o l a r i z

ed l i g h t r e f l e c t e d from th e p o le o f a n e le c t r o m a g n e t ) . The Zeeman

e f f e c t w i l l b e d i s c u s s e d i n s l i g h t l y m ore d e t a i l i n C h a p te r I I

b e c a u s e i t i s o f c o n s id e r a b le im p o r ta n c e i n t h e th e o r y o f th e

F a ra d a y e f f e c t . A l l f o u r o f th e s e m a g n e to o p tic e f f e c t s a r e d i s -2

c u s se d i n an e le m e n ta ry f a s h i o n by J e n k in s and W hite .

A cadem ic s t u d i e s o f th e F a ra d a y e f f e c t a r e l a r g e l y m o tiv a te d

by t h e hope t h a t t h e F a ra d a y e f f e c t w i l l p ro v e t o b e o f v a lu e a s

a t o o l f o r a n a ly z in g th e m o le c u la r s t r u c t u r e o f com pounds. I f

t h i s end i s t o b e r e a l i z e d , th e c o l l e c t i o n o f a c c u r a te s p e c t r a

from know n com pounds i s n e c e s s a r y . The p u rp o se o f t h i s work was

1


t o d e s ig n , c o n s t r u c t and e v a lu a te an in s t r u m e n t f o r m e a s u r in g th e

F a ra d a y r o t a t i o n a n d , i f s u c c e s s f u l , m easu re th e r o t a t i o n s p e c t r a

o f a s m a ll num ber o f com pounds.

P r o p e r t i e s

T h is t r e a tm e n t o f th e g e n e r a l p r o p e r t i e s o f th e F a ra d a y

e f f e c t f o l lo w s g e n e r a l ly t h a t o f P a r t i n g to n , An A dvanced T r e a t i s e

on P h y s i c a l C h e m is try , pp.. 5 9 2 -6 3 2 .

The f u n c t i o n a l d ep en d en ce o f th e r o t a t i o n p ro p o se d by F a ra d a y

was s u b s e q u e n t ly v e r i f i e d by V e r d e t , who p ro p o se d th e f o l lo w in g

e q u a tio n :

© i V J t H C o s $ f

W here 0 i s th e r o t a t i o n , J f t h e p a th l e n g t h , ^ th e a n g le b e tw e en

th e l i g h t r a y and th e f i e l d and H th e a p p l ie d m a g n e tic f i e l d

s t r e n g t h . V i s c o n s ta n t a t a g iv e n w a v e len g th and te m p e ra tu re

and i s u s u a l l y c a l l e d th e V e rd e t c o n s t a n t . V i s , o f c o u r s e ,

c h a r a c t e r i s t i c o f th e m a t e r i a l u s e d . V i s u s u a l l y ta k e n to be

p o s i t i v e i f th e r o t a t i o n i s i n th e same d i r e c t i o n a s th e c u r r e n t

w hich p ro d u ce d th e f i e l d and n e g a t iv e i f th e r o t a t i o n i s i n th e

o p p o s i te d i r e c t i o n . An im p o r ta n t f a c t i s t h a t e q u a t io n ( l ) can

n o t be w r i t t e n as a s im p le d o t p r o d u c t be tw een and H b e c a u s e

r e v e r s in g th e d i r e c t i o n o f l i g h t t r a v e l th ro u g h th e magnetic.-

f i e l d does n o t change th e s ig n o f th e r o t a t i o n , b u t r e v e r s in g

t h e d i r e c t i o n o f th e m a g n e tic f i e l d d o es change th e s ig n o f th e

r o t a t i o n .

H ot s u p r i s i n g l y , th e F a ra d a y e f f e c t has b e e n fo u n d t o o c c u r


4o v e r a l a r g e ra n g e o f w a v e le n g th s , in c lu d in g X -ra y s and

m icrow aves'* , b u t s y s te m a t ic i n v e s t i g a t i o n a p p e a rs t o have b e e n

c o n f in e d t o th e o p t i c a l and m icrow ave r e g i o n s . The i n f r a r e d

F a ra d a y e f f e c t i s o f some im p o r ta n c e i n t h e s tu d y o f in te r b a n d

e f f e c t s i n s e m ic o n d u c to rs and th e r a d io wave F a ra d a y e f f e c t c a n

be u s e d to s tu d y i n t e r s t e l l e r m a g n e tic f i e l d s ^ . The A p r i l , 1 9 6 7 ,

i s s u e o f A p p lied O p tic s c o n ta in s a num ber o f re v ie w a r t i c l e s on

m a g n e to o p tic e f f e c t s , i n c lu d in g th o s e i n s e m ic o n d u c to rs . The

work r e p o r te d o n i n t h i s t h e s i s was c a r r i e d o u t e n t i r e l y i n th e

v i s i b l e and n e a r u l t r a v i o l e t p o r t i o n s o f th e sp e c tru m .

The in f lu e n c e o f te m p e ra tu re on th e F a ra d a y e f f e c t i s some

w hat com plex . O ver ra n g e s o f a few d e g re e s a t room te m p e ra tu re ,

th e te m p e ra tu re dependence i s q u i t e s m a ll and c a n o f t e n b e n e g l e c t

e d . O ver a w ide te m p e ra tu re r a n g e , su ch a s from 1° K to room

te m p e ra tu re , s t r i k i n g ch an g es i n th e r o t a t i o n c an b e o b s e rv e d ,

p a r t i c u l a r l y i n th e c a s e o f p a ra m a g n e tic i o n s . T h is p ro b lem w i l l

b e d is c u s s e d l a t e r i n th e th e o ry s e c t i o n .

V e rd e t n o t ic e d t h a t th e r o t a t i o n s due to p a ra m a g n e tic io n s

( s u c h a s c o b a l t , n i c k e l and i r o n ) a r e i n th e o p p o s i te d i r e c t i o n

from t h a t o f w a te r . K undt d e te rm in e d t h a t i n t h i s c a s e th e r o t a

t i o n i s p r o p o r t io n a l t o th e m a g n e t iz a t io n , M, o f th e sa m p le , i . e . ,

& * KL.M ( 2)

Where K i s c a l l e d K u n d t1s c o n s ta n t and i s t h e sam ple p a th l e n g t h .

A g a in , t h i s e q u a t io n a p p l i e s a t a c o n s ta n t w a v e le n g th f o r a g iv e n

m a t e r i a l . The te m p e ra tu re dependence i s e s s e n t i a l l y d e te rm in e d

by th e te m p e ra tu re dependence o f M.


F e rro m a g n e tic m a t e r i a l s have a l s o been s tu d i e d . K und t found

l a r g e p o s i t i v e r o t a t i o n s i n t h in f i lm s o f i r o n . F o r exam ple,

u n d e r c o n d i t io n s su ch t h a t q u a r tz showed a r o t a t i o n o f a b o u t 20

d e g r e e s , a t h i n f i lm o f i r o n e x h ib i t e d a r o t a t i o n o f a b o u t 60

co m p le te r e v o l u t io n s .

The d i s p e r s io n , o r w a v e le n g th d e p e n d en c e , o f th e F a ra d a y

e f f e c t h a s b e e n s tu d i e d e x te n s iv e ly i n r e g io n s f a r from a b s o r p t io n s .

I n t h i s c a s e , th e d i s p e r s io n c a n u s u a l l y b e e x p re s s e d a s a power

s e r i e s i n ^ , much a s in d e x o f r e f r a c t i o n c u rv e s a re e x p re s s e d .

The i n t e r e s t i n g c a s e o c c u rs i f th e r o t a t i o n i s m easu red n e a r

o r i n an ̂ a b s o r p t io n r e g i o n . S e v e ra l s t u d i e s o f t h i s ty p e have7

b e e n c a r r i e d o u t . R. W. Wood d e s c r ib e s s e v e r a l e x p e r im e n ts done

by Zeeman w ith sodium f la m e s . Zeeman fo u n d anom alous e f f e c t s

a t th e ed g es o f a b s o r p t io n b a n d s , b u t saw n o th in g i n th e b a n d s

th § ® s?} v es .g

R e c e n tly , S hashoua h a s a p p l i e d m odern e l e c t r o n i c m ethods to

t h e s tu d y o f th e F a ra d a y e f f e c t i n a b s o r p t io n b an d s and h a s pub

l i s h e d a num ber o f anom alous d i s p e r s io n c u r v e s . S in c e th e b u lk

o f th e work r e p o r te d i n t h i s t h e s i s c o n c e rn s t h e F a ra d a y e f f e c t i n

a b s o r p t io n b a n d s , S hashoua*s work w i l l be d i s c u s s e d i n m ore d e t a i l

i n C h a p te r I I .

Some A p p l ic a t io n s

An i n t e r e s t i n g a p p l i c a t i o n o f t h e F a ra d a y e f f e c t i s t h a t o f

m e a su r in g i n t e r s t e l l a r m a g n e tic f i e l d s . The f i e l d s in v o lv e d sire

much to o s m a ll to p ro d u c e s i g n i f i c a n t o p t i c a l r o t a t i o n s ( u n l e s s


5

t h e l i g h t p a s s e s th ro u g h a l a r g e am ount o f i n t e r s t e l l a r d u s t o r

g a s ) , "but a t r a d i o w a v e le n g th s t h i s i s n o t t h e c a se « I n p a r t i c u l a r ,

Davies** h i s c o l l e a g u e s h av e m easu red th e o r i e n t a t i o n o f th e

p la n e o f p o l a r i z a t i o n o f l i g h t e m i t te d by s e v e r a l s t e l l a r o b j e c t s

a t w a v e le n g th s u p t o one m e te r . The f a c t t h a t one i s o b s e rv in g

F a ra d a y r o t a t i o n i s d e te rm in e d by th e in d e p e n d e n c e o f t h e - o r i e n t a

t i o n . E x t r a p o l a t i o n t o z e ro w a v e le n g th p ro d u c e s a v a lu e f o r th e

r o t a t i o n . I f one m akes some a s su m p tio n s a b o u t t h e d e n s i ty o f

i n t e r s t e l l a r d u s t and g a s , t h e s i z e o f th e m a g n e tic f i e l d i n th e

g a la x y c a n b e d e te rm in e d . The v a lu e a p p e a rs t o l i e i n th e ra n g e

o f 10“ 4 t o 10” ** g a u s s .q

H c C a rta n and B a r r a u l t r e c e n t l y d e s c r ib e d a sy s te m u s in g th e

F a ra d a y e f f e c t t o m easu re t h e m a g n e tic f i e l d s i n a p la sm a . They

s im p ly p la c e d a s m a ll g l a s s c y l i n d e r i n t h e r e g io n t o be t e s t e d

an d m easu red t h e F a ra d a y r o t a t i o n o f th e beam o f l i g h t fro m a

l a s e r . T h is m ethod a l lo w s a v e ry s m a ll p r o b e , w i th no e l e c t r i c a l

c o n n e c t io n s , t o b e u s e d .

The F a ra d a y e f f e c t may a l s o b e u s e d a s a n a id i n i t s own

m easu rem en t and i n t h e m easurem ent o f o p t i c a l r o t a t o r y d i s p e r s io n .

I f one w rap s a c o i l o f w ire a ro u n d a c y l i n d r i c a l Bample and p a s s e s

a - c th ro u g h th e w i r e , th e p la n e o f p o l a r i z a t i o n o f th e t r a n s m i t t e d

l i g h t w i l l o s c i l l a t e . By a r r a n g in g a s e rv o sy s te m t o a d j u s t th e

a n a ly z e r u n t i l t h e two e x c u r s io n s a re e q u a l , r o t a t i o n s c a n be

m e a su re d .


CHAPTER I I

-■ THEORY

A ttem p ts to e x p la in th e F a ra d a y e f f e c t g e n e r a l ly b e g in w ith

t h e i d e a t h a t a p la n e p o la r i z e d wave may h e decom posed i n t o two

c i r c u l a r l y p o l a r i z e d waves r o t a t i n g i n o p p o s i te d i r e c t i o n s . A

l i t t l e th o u g h t w i l l c o n v in c e one t h a t i f th e r e l a t i v e p h a se d i f

f e r e n c e b e tw een th e two waves c h a n g e s , th e p la n e o f p o l a r i z a t i o n

w i l l b e changed by an amount p r o p o r t io n a l to th e change i n p h a s e .

I f one assum es t h a t th e m a g n e tic f i e l d a c t i n g on th e m o le c u le s o f

th e sam ple somehow p ro d u c e s a r e l a t i v e p h a se d i f f e r e n c e be tw een

th e two c i r c u l a r l y p o l a r i z e d com ponen ts , th e n many q u a l i t a t i v e

f e a t u r e s o f th e F a rad a y e f f e c t may b e e x p la in e d . The m echanism

t h a t a llo w s a r e l a t i v e p h ase d i f f e r e n c e to be d e v e lo p e d i s th e

Zeeman e f f e c t ; t h e r e f o r e , a l l a t te m p ts to c a l c u l a t e th e F a rad a y

r o t a t i o n b e g in h e r e .

I n te rm s o f c a l c u l a t i n g th e F a ra d a y e f f e c t q u a n t i t a t i v e l y ,

one f in d s t h a t a c o m p le te quantum m e c h a n ic a l t r e a tm e n t i s n e c e s s a r y .

T h is in c lu d e s th e d i s p e r s io n fo rm u la f o r th e in d e x o f r e f r a c t i o n

t h a t i s u s e d , s in c e m ost such fo rm u la e do n o t rem a in f i n i t e a t

th e r e g io n o f a b s o r p t io n . Such a c a l c u l a t i o n w i l l n o t be a tte m p te d

h e r e .

The f a c t t h a t some s im p le and e v e n a p p ro x im a te ly c o r r e c t

e x p re s s io n s can. be c a lc u la t e d c l a s s i c a l l y i s o f some i n t e r e s t .

B e e q u e re l ( d e s c r ib e d by P a r t i n g to n ) i n 1897 p ro p o se d such a n

e q u a t io n . He e s s e n t i a l l y assum ed th e e t h e r t o be r o t a t i n g w ith a

6


c o n s ta n t a n g u la r v e l o c i t y w h ich he d e te rm in e d from th e known s i z e

o f th e Zeeman e f f e c t : . H is r e s u l t i s :

& = ( c o n s t a n t ) ( d n /d ^ ) (5 )

L arm or l a t e r d e te rm in e d t h a t th e c o n s ta n t i s e q u a l to e/2m e,

and t h i s e q u a t io n , w i th an a p p r o p r i a t e d i s p e r s io n e q u a t io n f o r

d n /d > , does a p p e a r to work f a r from an a b s o r p t io n r e g io n .

Zeeman E f f e c t

The Zeeman e f f e c t i s , o f c o u r s e , t h e s p l i t t i n g o f s p e c t r a l

l i n e s i n a m a g n e tic f i e l d . The Zeeman e f f e c t o c c u rs b o th on

e m is s io n and a b s o r p t io n ; t h e l a t t e r c a s e i s som etim es c a l l e d th e

in v e r s e Zeeman, e f f e c t .

I n th e c a s e o f th e s o - c a l l e d "no rm al" Zeeman e f f e c t , a l l

s p e c t r a l l i n e s a p p e a r to be s p l i t i n t o t h r e e p la n e p o l a r i z e d com

p o n e n ts when v iew ed p e r p e n d ic u l a r to th e f i e l d and i n t o two

c i r c u l a r i s e p o l a r i z e d com ponents when v iew ed p a r a l l e l to th e f i e l d .

The no rm al Zeeman e f f e c t i s o b se rv e d e i t h e r when th e m a g n e tic f i e l d

a p p lie d to th e sam ple i s s t r o n g enough to o v e r r id e th e i n t e r n a l

a to m ic o r m o le c u la r f i e l d s o r when th e t o t a l s p in o f t h e s t a t e

i s e q u a l to z e ro . I n th e fo rm e r c a s e th e e f f e c t i s u s u a l l y c a l l e d2

th e P a sc h en -B a c k e f f e c t . The s p l i t t i n g goes a s , w here 7 \ i s

th e w a v e le n g th o f th e u n s p l i t l i n e .

I n t h e c a s e o f h ig h e r s p in s t a t e s ( w i th low enough a p p l i e d

f i e l d ) th e num ber o f l e v e l s g o e s a s j ( j +■ l ) , w here J i s t h e

t o t a l a n g u la r momentum quantum num ber, and th e p a t t e r n i s no

lo n g e r s im p le .


8

Q u a l i t a t i v e D e te rm in a t io n s o f R o ta t io n s

A v e ry s im p le p h y s ic a l p i c t u r e ; b a s e d on th e Zeeman e f f e c t ,

w h ich a llo w s th e q u a l i t a t i v e f e a t u r e s o f F a ra d a y r o t a t i o n s p e c t r a

t o b e u n d e rs to o d was in t r o d u c e d by Zeeman and i s d i s c u s s e d i n some

d e t a i l by R. W. Wood10 ,

One b e g in s by assu m in g t h a t t h e no rm al Zeeman e f f e c t s p l i t s

an a b s o rp t io n : l i n e i n t o two com ponen ts , e a c h o f w hich a b s o rb s

c i r c u l a r l y p o l a r i z e d l i g h t o f a g iv e n d i r e c t i o n o f r o t a t i o n .

The r e s u l t w i l l be two d i s p e r s io n c u rv e s t r a n s l a t e d i n w a v e le n g th

( b e c a u s e o f th e Zeeman s p l i t t i n g ) w ith r e s p e c t to e a c h o t h e r .

F i r s t assum e t h a t th e two c u rv e s have e q u a l a m p l i tu d e , a s shown

in . F ig u r e 1 ( a ) . O u ts id e t h e a b s o r p t io n r e g io n , th e ccw compon

e n t h a s th e h ig h e r in d e x o f r e f r a c t i o n and h e n c e m oves s lo w e r .

I n s i d e th e a b s o r p t io n b and th e cw com ponent h a s th e h ig h e r in d e x

and th e s lo w e r s p e e d . T hus, a r o t a t i o n v e r s u s w a v e le n g th c u rv e

s i m i l a r to F ig u r e 1 (b ) m ig h t b e e x p e c te d .

I f , how ever, th e two c u rv e s have d i f f e r e n t a m p l i tu d e s , a s

i n F ig u re 2 ( a ) , t h e r e s u l t i n g r o t a t i o n c an ta k e th e form i n d i c a t

ed i n F ig u re 2 ( b ) . Y a r io u s c o m b in a tio n s i n b e tw e en a r e a ls o

p o s s i b l e . S p e c t r a o f th e ty p e i n F ig u re 1 (b ) w i l l b e c a l l e d

ty p e I s p e c t r a and s p e c t r a o f th e ty p e i n F ig u r e 2 (b ) w i l l be

r e fe n m d to a s ty p e I I s p e c t r a i n th e r e s t o f t h i s t h e s i s .

TJnder w hat c o n d i t io n s w ould e .eh o f th e s e ty p e s o f s p e c t r a

be e x p e c te d to o c c u r? I f one assum es t h a t e l e c t r o n s w ith s p in

up t r a n s m i t c i r c u l a r l y p o l a r i z e d l i g h t o f one o r i e n t a t i o n and

e l e c t r o n s w ith s p in down t r a n s m i t th e o th e r o r i e n t a t i o n , some


A TYPE I SPECTRUM

■cw

W avelength

0W avelength

•H

«

FIGURE 1

A TYPE I I SPECTRUM

W -Pyi'0 W avelength

0W avelength•rl

FIGURE 2


10

p r e d i c t i o n s c an be made.

D ia m a g n e tic io n s a r e c h a r a c te r iz e d by th e f a c t t h a t th e

e l e c t r o n s have no te n d e n c y to a l i g n i n an e x te r n a l m a g n e tic f i e l d .

The o r b i t a l m o tio n i s s im p ly a l t e r e d ( f o l lo w in g Lenz* s law ; i n

su c h a way a s to p ro d u ce a weak m ag n e tic moment o p p o s i te to th e '

d i r e c t i o n , o f t h e a p p l ie d f i e l d . The e le c t r o n s a r e a l l p a i r e d o f f

and rem a in t h a t way, so t h a t one m igh t e x p e c t a ty p e I sp e c tru m

i n t h i s c a s e .

On th e o th e r h an d , p a ra m a g n e tic io n s a re c h a r a c te r i z e d by

u n p a ir e d e l e c t r o n s w h ich may a l i g n i n an e x te r n a l a p p l ie d m agnet

i c f i e l d . T herm al e f f e c t s te n d to d i s a l i g n th e e l e c t r o n s p in s ,

b u t even a t room te m p e ra tu re a sm a ll p o s i t i v e m ag n e tic moment can

be o b s e rv e d . T h u s , one may e x p e c t to f in d a d i f f e r e n t num ber o f

e l e c t r o n s w ith s p in up t h a n w ith s p in down; a ty p e I I sp e c tru m

m ig h t be o b ta in e d . N o te , t h a t i f a l l t h e e l e c t r o n s ( u n p a i r e d )

a r e a l i g n e d , th e n o n ly one d i s p e r s io n c u rv e o f th e in d e x o f

r e f r a c t i o n w i l l be o b ta in e d . No anom alous d i s p e r s io n o f th e

F a ra d a y e f f e c t w i l l be o b se rv e d i n t h i s ca se*

T e m p era tu re e f f e c t s may be q u i t e im p o r ta n t i n t h e c a s e o f

p a ra m a g n e tic i o n s . The s u s c e p t i b i l i t y o f many p a ra m a g n e tic io n s

fo l lo w s What i s know nss th e C u rie -W eiss law , _i. _e. ,th e s u s c e p t

i b i l i t y i s p r o p o r t io n a l • T i s th e a b s o lu te te m p e ra tu re

and © i s a c o n s ta h t , w i th u n i t s o f te m p e ra tu re , c h a r a c t e r i s t i c ® f th e

io n . T hus, i f th e s u s c e p t i b i l i t y o f th e io n f o l lo w s a C u rie -W eiss

la w , n e a r th e c h a r a c t e r i s t i c te m p e ra tu re © th e e l e c t r o n s w i l l

b e n e a r ly a l l a l ig n e d and o n ly a s m a ll anom alous e f f e c t w i l l be

o b s e rv e d .


11

E x p e r im e n ta l E v id en ce

8The work m en tio n e d e a r l i e r hy S hashoua c o n ta in s a num ber o f

exam ples o f p a ra m a g n e tic and d ia m a g n e tic io n s i n s o l u t i o n . He

o b ta in e d a ty p e I sp e c tru m f o r m ost d ia m a g n e tic o r g a n ic com pounds,

exam ples b e in g p h e n a z in e , a c e to n e , f lu o r e n e , e a r b a z o le and e th y l

ene t r i t h i o c a r b o n a t e . He o b ta in e d a ty p e I I sp e c tru m from p a r a

m a g n e tic compounds su c h a s f e r r i c c h lo r id e and v a r io u s c o b a l t

com pounds. N ic k e l s u l f a t e p ro d u ce d o n ly an o r d in a r y d i s p e r s i o n

c u rv e . A num ber o f compounds showed d i f f e r e n t ty p e s o f s p e c t r a

a t d i f f e r e n t a b s o r p t io n b a n d s , w hich o n ly i n d i c a t e s th e in a d e q u a c y

o f t h e m odel h e re p r e s e n te d .

L o v in g ^ o b se rv e d a num ber o f i n t e r e s t i n g e f f e c t s w ith

n i c k e l s u l f a t e . Among th e s e w ere : ( l ) a ty p e I s p e c tru m , (2 ) t h e

s i z e o f th e e f f e c t was n o t l i n e a r w i th c o n c e n t r a t io n , ( 3) no

e f f e c t a t a l l was o b se rv e d w ith v e ry low c o n c e n t r a t io n s .

12B r i a t o b se rv e d a ty p e I s p e c tru m i n CoCl^ i a aqueous

s o l u t i o n . He a l s o o b se rv e d a ty p e I I sp e c tru m i n m e th y lp r o p y l ie -

13to n e . B r i a t a l s o m easu red t h e r o t a t i o n o f th e f e r r i c y a n i d e io n

and o b ta in e d a ty p e I I sp e c tru m

V o lk e n s te in , e t . a l . ^ , o b ta in e d ty p e I s p e c t r a f o r h em o g lo b in

and m y o g lo b in a t th e lo n g w a v e le n g th (5500 -6000 A) band and ty p e

I I s p e c t r a a t th e s h o r t (4200 A) w a v e len g th b a n d . The s p e c t r a

f o r o x y g e n a te d h em o g lo b in and m y o g lo b in was t h e same., q u a l i t a t i v e l y

b u t n o t q u a n t i t a t i v e l y , i n d i c a t i n g t h a t m o le c u la r s t r u c t u r e i s o f

some im p o r ta n c e f o r d e te rm in in g th e anom alous d i s p e r s io n c u rv e

f o r th e F a ra d a y e f f e c t . No a t te m p t w i l l be made to d i s c u s s h e re


12

th e r e l a t i v e s i z e s o f th e r o t a t i o n s o b ta in e d , e x c e p t t o m e n tio n

t h a t , b a s e d on S h a sh o u a 1 s w ork , t h e r e do n o t a p p e a r t o b e any

d e f i n i t e p a t t e r n s .

S e l e c t io n o f Compounds to be S tu d ie d

The two m ain g ro u p s o f io n s w h ich m ig h t be o f i n t e r e s t a r e

th o s e from th e r a r e e a r t h g roup and t h e i r o n g ro u p , A t a b l e

15su c h a s t h a t fo rm in g F ig u r e 3 , re p ro d u c e d from M o rr is h , i s

h e l p f u l . T h is t a b l e i s e s s e n t i a l l y a l i s t i n g o f t h e i r o n g ro u p

i o n s by m a g n e tic moment, w i th th e i o n h a v in g th e l a r g e s t m ag n e tic

moment b e in g l i s t e d i n t h e c e n te r o f th e t a b l e . One w ould p ro b a b

l y w ant t o m easu re t h e s p e c t r a o f io n s r e p r e s e n t i n g a l l s e c t i o n s

o f t h e t a b l e .

F in d in g a s u i t a b l e d ia m a g n e tic compound i s d i f f i c u l t s in c e

t h e l a c k o f u n p a ir e d e l e c t r o n s u s u a l l y means t h a t a b s o r p t io n does

n o t o c c u r u n t i l th e f a r u l t r a v i o l e t p o r t i o n o f th e s p e c tru m .

P o ta s s iu m i o d id e , h o w ev er, a b s o rb s a t a b o u t 3600 A and h ence

m ig h t b e a s u i t a b l e r e p r e s e n t a t i v e o f th e d ia m a g n e tic io n s l i s t e d

i n F ig u re 3 ,

N ic k e l s u l f a t e w ould b e i n t e r e s t i n g b e c a u s e , i f S h ash o u a1s

m easu rem en ts a r e c o r r e c t , t h i s compound d o e s n o t f i t i n t o th e

s im p le p i c t u r e p r e s e n te d ab o v e ,

C u p ric s u l f a t e m ig h t a l s o b e a good m o le c u le t o t r y s in c e i t- . - jt2 4 2

a b s o rb s i n th e v i s i b l e . A ls o , SuT l i e s n e a r Ni i n F ig u r e , 3»*

F e r r i c c h l o r i d e l i e s i n th e c e n t e r o f th e t a b l e and shows

l a r g e r o t a t i o n s . I t w ould a l s o b e a good compound to t r y .


LIST OF IRON GROUP IONS

ION

K+ r Ca34 D ia m ag n e tic

T i3 4 , V4* 1 .7

7 34 2 .8

V2* , Cr3 4 , Kn44 3 .8

C r2+, Mn34 4 .9

Mn2\ F e 3+ 5 .9

F e 2+ 5 .4

Co24 4 .8

N i24 3 .2

Cu2+ 1 .9

Cu4 , Zn24 D ia m a g n e tic

FIGURE 3


CHAPTER I I I

EXPERIMENTAL METHODS

I n t h i s s e c t i o n , a v a r i e t y o f m ethods f o r s tu d y in g th e F a ra d a y

e f f e c t w i l l "be o u t l i n e d . C e r ta in ones w i l l h e exam ined i n c l o s e r

d e t a i l , e s p e c i a l l y w ith r e g a r d t o e x p e r im e n ta l u n c e r t a i n t y and

s e n s i t i v i t y .

The s tu d y o f th e F a ra d a y e f f e c t h as p r o f i t e d from th e c o n s id

e r a b le te c h n o lo g y d e v e lo p e d f o r th e s tu d y o f o p t i c a l r o t a t o r y d i s

p e r s io n ( ord) .

N o n - e le e tr o n ic M ethods

T h ere a r e a num ber o f n o n - e l e c t r o n ic m ethods a v a i l a b l e . The

ones d e v e lo p e d s p e c i f i c a l l y f o r th e s tu d y o f ORD a re d e s c r ib e d i n

Lowry^.The m ost s t r a ig h t f o r w a r d , o f c o u r s e , i s t h a t p i c t u r e d i n

F ig u re 4 . One b e g in s w ith th e p o l a r i z e r and a n a ly z e r c r o s s e d ,

tu r n s on th e f i e l d , and th e n r o t a t e s th e a n a ly z e r f o r e x t i n c t i o n .

T h is m ethod s u f f e r s from a num ber o f d is a d v a n ta g e s , th e m ain ones

b e in g ( l ) th e ra n g e o f w a v e le n g th s w hich c an b e s tu d i e d i s l im i t e d

t o th e re s p o n s e o f th e human eye and ( 2) t h e s e n s i t i v i t y i s low

b e c a u se e s t im a t in g th e p o in t o f e x t i n c t i o n to b e t t e r th a n a few

t e n t h s o f a d e g re e i s q u i t e d i f f i c u l t .

The n e x t s te p i n th e im provem ent o f th e s im p le v i s u a l sy stem

i s th e h a l f - s h a d e sy s te m . I n t h i s c a s e , th e p o l a r i z e r i s made i n

14


tw o s e c t io n s w hich a r e r o t a t e d s l i g h t l y w ith r e s p e c t to e a ch o t h e r

When lo o k in g th ro u g h th e a n a ly z e r , one s e e s a p a t t e r n s i m i l a r to

t h a t o f F ig u re 5 . The a n a ly z e r i s a d ju s t e d i n i t i a l l y f o r e q u a l

i n t e n s i t i e s i n e a ch h a l f o f t h e f i e l d o f v iew . The f i e l d i s

tu rn e d on and th e a n a ly z e r r e ,a d ju s te d f o r e q u a l i n t e n s i t i e s . Be

c a u s e th e ey e c an m atch th e i n t e n s i t i e s o f two f i e l d s o f v iew

moie e a s i l y th a n i t c a n l o c a t e a minimum, t h i s m ethod i s s e n s i t i v e

17to n e a r ly 0 .003 d e g re e . S e n s i t i v i t y o f t h i s o r d e r c an he

a c h ie v e d o n ly hy a v e ry good o b s e rv e r u n d e r th e b e s t p o s s ib l e

c o n d i t io n s .

O c c a s io n a l ly th e f i e l d o f v iew i s d iv id e d i n t o t h r e e s e c t i o n s

b u t t h i s seem s to o f f e r l i t t l e a d v a n ta g e o v e r th e h a l f - s h a d e

sy s te m .

The p r im a ry im p o rta n c e o f th e h a l f sh a d e sy s tem to th e p r e

s e n t work i s th e f a c t t h a t i t c a n be e a s i l y a d a p te d to p h o to

e l e c t r i c i n s t r u m e n ta t io n . T h is w i l l be d i s c u s s e d i n th e n e x t

s e c t i o n .

S e v e ra l i n t e r f e r o m e t r i c sy s te m s w ere d e v e lo p e d i n th e e a r l y

18p a r t o f t h i s c e n tu ry . Of p a r t i c u l a r im p o r ta n c e i s th e S a v a r t

19P l a t e . I n t h i s c a s e , th e p o l a r i z e r i s a d ju s t e d i n su c h a

m anner t h a t th e i n t e r f e r e n c e f r i n g e s d i s a p p e a r from t h e c e n t e r o f

th e f i e l d o f v iew . The m a g n e tic f i e l d i s t u r n e d on and th e

p o l a r i z e r r o t a t e d u n t i l th e f r i n g e s a g a in d i s a p p e a r . T h is m ethod

may d e t e c t r o t a t i o n s a s sm a ll a s 0 .0 1 d e g re e .

The w a v e len g th l i m i t a t i o n s o f th e human eye c a n o f t e n be

overcom e by th e u s e o f p h o to g ra p h ic te c h n iq u e s . E m u ls io n s a r e


A METHOD OF STUDYING THE FARADAY EFFECT

- - B - -Lamp P o l a r i z e r

— 0—A n a ly zer

-«>Eye

Magnet

FIGURE k

FIELD OF VIEW WITH A HALF-SHADE POLARIZER

FIGURE 5

USE OF THE SAVART PLATE

&Lamp

f l -P o l a r i z e r

Magnet

FIGURE 6

B -0-----^S a v a r t A n a ly zer Eye P l a te


a v a i l a b l e f o r work from th e u l t r a v i o l e t to th e i n f r a r e d , b u t one

i s u s u a l l y f a c e d w ith th e n e c e s s i ty o f a n a ly z in g th e r e s u l t a n t

p l a t e w i th some s o r t o f m ic ro p h o to m e te r o r d e n s i to m e te r and t h i s

c a n n o t o f t e n be done w ith ex trem e a c c u ra c y .20

The h a l f - s h a d e m ethod h a s b e e n e x te n d e d t o p h o to g ra p h y

w ith e x c e l l e n t r e s u l t s — e x p e r im e n ta l e r r o r s on th e o r d e r o f 0 .0 2

d e g re e have b e e n re -p o r te d . I n t h i s c a s e one i s r e a l l y m e a su r in g

w a v e le n g th a s a f u n c t io n o f r o t a t i o n , r a t h e r th a n v i c e - v e r s a ,

s in c e one e s s e n t i a l l y lo o k s f o r s p e c t r a l l i n e s w hich have th e

same i n t e n s i t y i n b o th h a lv e s o f th e f i e l d o f v iew ( a s re c o rd e d

on a p h o to g ra p h ic p l a t e ) .

A n o th e r p h o to g ra p h ic m ethod was d e v e lo p e d by L o v in g 1 1 . A

s e r i e s o f p h o to g ra p h ic s p e c t r a o f a c o n tin u o u s l i g h t s o u rc e a re

made f o r d i f f e r e n t a n a ly z e r p o s i t i o n s . The a n a ly z e r i s th e n

r e tu r n e d to th e z e ro p o s i t i o n and a n e x p o su re made w ith th e mag

n e t i c f i e l d on . The p l a t e b la c k e n in g a t a g iv e n w a v e le n g th w ith

t h e f i e l d on i s com pared w ith th e r e f e r e n c e s p e c t r a u n t i l one

w i th t h e same b la c k e n in g i s fo u n d . The p o s i t i o n o f th e a n a ly z e r

f o r t h a t p a r t i c u l a r r e f e r e n c e sp e c tru m g iv e s th e r o t a t i o n f o r

t h a t w a v e le n g th . I n p r a c t i c e , t h i s m ethod h a s b e e n a c c u r a te to

a b o u t 0 .5 d e g re e .

I n summary one c o u ld say t h a t p h o to g ra p h ic m e th o d s , i f p e r

fo rm ed w ith s u f f i c i e n t c a r e , can y i e ld v e ry good r e s u l t s . The

m ain d is a d v a n ta g e s p ro b a b ly a r e th e lo n g ex p o su re t im e s and th e

tim e r e q u i r e d i n a n a ly z in g th e p l a t e . I f p o s s ib l e , one would

l i k e t o be a b le to u s e a m ethod w hich g iv e s th e r o t a t i o n d i r e c t l y ,


18

r a t h e r th a n as th e r e s u l t o f a s e r i e s o f in te r m e d ia t e s t e p s .

E l e c t r o n i c M ethods

The s im p le s t p h o t o e l e c t r i c p o l a r im e te r w ould c o n s i s t o f

r e p l a c i n g th e eye in . F ig u re 4 w ith an a p p r o p r ia t e p h o to tu b e . The

w a v e le n g th l i m i t a t i o n e x i s t i n g b e f o r e i s now rem oved, and th e

s e n s i t i v i t y ca n b e in c r e a s e d a lm o s t a t w i l l . H ow ever, s e v e r a l

o th e r p ro b le m s a r i s e . One p rob lem i s th e f a c t t h a t t h e i n t e n s i t y

o f th e l i g h t t r a n s m i t t e d a t e x t i n c t i o n c a n n o t be re d u c e d t o z e ro

b e c a u s e , f o r exam ple, th e l i g h t i n c i d e n t on th e a n a ly z e r may n o t

b e c o m p le te ly p la n e p o l a r i z e d . A n o th e r p o s s i b i l i t y i s t h a t some

l i g h t may b e s c a t t e r e d from th e o p t i c a l s u r f a c e s i n th e s y s te m .

I n any c a s e , l o c a t i o n o f th e minimum i s n o t e a s y .

As m en tio n e d e a r l i e r , th e h a l f - s h a d e sy stem may b e a d a p te d to

p h o t o e l e c t r i c i n s t r u m e n ta t io n . T h is may be a c c o m p lish e d by a llo w

in g th e l i g h t from e a c h h a l f o f th e f i e l d o f v iew to f a l l on a

p h o to tu b e . Then a t b a la n c e , th e o u tp u ts o f th e two p h o to tu b e s w i l l

be e q u a l and chan g es i n th e i n t e n s i t y o f th e s o u rc e w i l l n o t

have undue e f f e c t s . A more p r a c t i c a l ap p ro a c h i s to a l lo w l i g h t

from e a ch h a l f o f th e f i e l d o f v iew t o f a l l a l t e r n a t e l y on th e

same p h o to tu b e . I n t h i s c a s e t h e r e w i l l be no a - c o u tp u t when

21th e sy s tem i s b a la n c e d . U s in g an a - c a p p ro a c h , Levy c o n s t r u c te d

am a u to m a tic a n g le m e a su r in g sy s te m f o r ORs work h a v in g a s e n

s i t i v i t y o f ab o u t 0 .0 0 5 d e g re e .

The s im p le p h o t o e l e c t r i c sy s tem d e s c r ib e d a t th e b e g in n in g

o f t h i s s e c t i o n can b e im proved c o n s id e r a b ly by th e a d d i t i o n o f


19

an o s c i l l a t i n g p o l a r i z e r . The i d e a b e h in d t h i s a r ra n g e m e n t i s

t h a t one c a n l o c a t e two p o i n t s on e i t h e r s id e o f th e minimum

w here th e i n t e n s i t i e s a r e e q u a l , and th e n p o s t u l a t e t h a t t h e a c t u a l

e x t i n c t i o n p o i n t l i e s h a lfw a y i n b e tw e e n . T h u s , t h e a n a ly z e r i s

s im p ly r o t a t e d u n t i l t h e o u tp u t v o l ta g e s a t th e two e x tre m e s o f

p o l a r i z e r m o tio n a r e e q u a l . S h a s h o u a 's m ethod u s e d an o s c i l l a t i n g

p o l a r i z e r ; s e n s i t i v i t y i n th e ra n g e from 0 .0 0 1 t o 0 .0 0 5 d e g re e

was o b ta in e d .

The n e x t o b v io u s s te p i s t o r e p l a c e th e m e c h a n ic a l ly o s c i l

l a t i n g p o l a r i z e r w i th a F a ra d a y c e l l , a s m en tio n e d e a r l i e r .

22S h a s h o u a 's seco n d sy s tem u s e s t h i s schem e and s e n s i t i v i t i e s c lo se s

t o 0 ,0 0 1 d e g re e h a v e b e e n r e p o r t e d by h im . He a l s o em ployed a n

in g e n io u s m ethod to s u b t r a c t o u t th e s o lv e n t r o t a t i o n , w h ich c o n

t r i b u t e s to th e low e r r o r . S in c e t h i s p ro b le m i s common t o a l l

m ethods o f m e a s u r in g th e F a ra d a y e f f e c t , i t w i l l b e d i s c u s s e d i n

C h a p te r V I I .

I n m aking any s o r t o f c o m p a riso n m ea su rem e n ts , one m ust

a lw a y s c o n s id e r d o u b le beam m ethods su c h a s th o s e t h a t h a v e b e e n

h ig h ly d e v e lo p e d f o r i n c o r p o r a t io n i n t o s p e c t r o p h o to m e te r s y s te m s .

S uch a sy s te m c an b e a d a p te d to th e s tu d y o f th e F a ra d a y e f f e c t ,

b u t few su c h sy s te m s a r e d e s c r ib e d i n th e l i t e r a t u r e . Two a r e

m en tio n e d b r i e f l y i n A p p lie d O p t i c s , 6 , 668 ( 1 9 6 7 ) . I n one c a s e ,

t h e r e l a t i v e p h a s e s o f th e two s i g n a l s a r e com pared . A r o t a t i n g

p o l a r i z e r i s u s e d . I n th e o t h e r , th e i n t e n s i t i e s o f t h e tw o

beam s a r e com pared w ith th e f i e l d on and o f f . A f ix e d p o l a r i z e r

and a n a ly z e r a rra n g e m e n t i s u se d and s ig n a l o u tp u t i s p r o p o r t i o n a l


20

t o t h e d i f f e r e n c e i n i n t e n s i t y b e tw een th e two beam s. I f

e x tr a n e o u s e f f e c t s h av e been e l im in a te d t h i s s ig n a l w i l l b e p ro

p o r t i o n a l to th e r o t a t i o n .

T h is l a s t m ethod i s e s s e n t i a l l y th e one c h o sen f o r t h i s s tu d y .

The p r im a ry r e a s o n was th e a p p a re n t l a c k o f work w ith t h i s ty p e

o f in s t r u m e n t , w h ich one would e x p e c t to be c a p a b le o f r e a s o n a b ly

h ig h s e n s i t i v i t y . The sy stem to be d e s c r ib e d i n more d e t a i l l a t e r

i s diagram m ed i n F ig u r e 7 . L ig h t from a c o n tin u o u s s o u rc e i s

p a s s e d th ro u g h a m onochrom ator and th e r e s u l t i n g l i g h t c o l l im a te d

by l e n s L . Upon p a s s in g th ro u g h th e p o l a r i z e r , th e beam i s a l

t e r n a t e l y a llo w e d to p a s s th ro u g h th e sam ple and a ro u n d i t . The

beam s a r e com bined a t th e p h o to tu b e , w here an a -c s ig n a l w hich

d epends on th e d i f f e r e n c e i n i n t e n s i t y o f th e two beams i s ob

t a i n e d . A d -c com ponent w h ich e s s e n t i a l l y m easu res th e t o t a l

l i g h t l e v e l i s a l s o o b ta in e d . I n o p e r a t io n , th e a n a ly z e r i s

f i r s t a d ju s t e d t o o b ta in z e ro a -c o u tp u t . The m a g n e tic f i e l d i s

tu rn e d on and th e a n a ly z e r r e a d j u s t e d f o r b a la n c e . The r o t a t i o n

may th e n be d e te rm in e d from th e c a l i b r a t e d a n a ly z e r s c a l e .


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CHAPTER I ?

DESIGN CONSIDERATIONS

One o f t h e c r i t i c a l p o in t s to be k e p t i n m ind when d e s ig n in g

a sy s te m s i m i l a r to t h a t o f F ig u r e 7 i s t h a t a n y th in g w h ich

ch a n g es th e r e l a t i v e i n t e n s i t y o f th e two beams w i l l show up i n

th e d a t a a s a r o t a t i o n . I n f a c t , a n y th in g i n th e a m p l i f i e r w hich

i n d i c a t e s th e p r e s e n c e o f a s ig n a l when t h e r e sh o u ld n o t be one

w i l l show up a s a r o t a t i o n .

T h is l e a d s one d i r e c t l y to th e c h o ic e o f a -c f o r th e s ig n a l

to be m e a su re d . A d -c sy s tem w ould r e q u i r e two p h o to tu b e s , each

o p e r a t in g i n t o one s id e o f a d i f f e r e n c e a m p l i f i e r . The d i f f e r e n c e

would t h e n b e fo llo w e d by s e v e r a l s ta g e s o f d -c a m p l i f i c a t i o n to

d r iv e a m e te r o f some s o r t . Any te n d e n c y o f t h e d -c a m p l i f i e r s

to d r i f t w ould show up a s a change i n th e r e l a t i v e i n t e n s i t i e s o f

th e two beam s. D i r e c t co u p led a m p l i f i e r s a re p ro n e to d r i f t i n g

b e c a u se th e y a m p lify d -c and d -c i s u s e d t o o p e r a te th em . T hus,

any change i n t h e pow er su p p ly v o l ta g e s w i l l show up a s an o u tp u t

s i g n a l . A d -c a m p l i f i e r c a n be s t a b l i z e d , b u t i t c a n n o t b e done

i n a s im p le m anner.

Changes i n th e pow er s u p p ly v o l ta g e s o f a n a -c a m p l i f i e r w i l l

change i t s g a in som ew hat, b u t w i l l n o t c o n t r i b u t e a n y th in g t o th e

o u tp u t s i g n a l .

I n s e l e c t i n g a ch o p p in g f re q u e n c y , 60 and 120 Hz s h o u ld be

a v o id e d s in c e th e s e f r e q u e n c ie s a r e p r e s e n t i n a l l pow er l i n e

o p e ra te d equ ipm en t t o some e x t e n t . A f re q u e n c y o f a b o u t 100 Hz i s

22


s a t i s f a c t o r y , s in c e i t l i e s ab o u t h a l f way b e tw e en 60 and 120 Hz.

T h e re a r e s e v e r a l m ethods o f d e t e c t i n g th e a - c o u tp u t s i g n a l .

S t r a ig h t f o r w a r d a m p l i f i c a t i o n and r e c t i f i c a t i o n i s o b v io u s ly n o t

s a t i s f a c t o r y a t low s i g n a l l e v e l s b e c a u s e o f n o i s e from v a r io u s

s o u rc e s and 60 and 120 Hz hum from th e pow er s u p p l i e s . C le a r ly ,

th e s ig n a l to n o i s e r a t i o c a n be im proved by r e d u c in g th e band

w id th s in c e n o i s e i s d i s t r i b u t e d a p p ro x im a te ly u n ifo rm ly th ro u g h

o u t th e f re q u e n c y s p e c tru m , b u t th e s ig n a l i s n o t . T h e re a re a t

l e a s t two ways o f r e d u c in g th e b a n d w ith . One i s th e u s e o f a

tu n e d a m p l i f i e r , made so t h a t th e t u n in g i s r e l a t i v e l y s h a r p ,

fo llo w e d by a r e c t i f i e r and a d -c m e te r .

The seco n d m ethod i s c a l l e d p h a se s e n s i t i v e d e t e c t i o n . I n

t h i s c a s e th e m e te r i s s w itc h e d b a c k and f o r t h a c r o s s th e o u tp u t

o f th e a m p l i f i e r a t t h e same r a t e th e l i g h t i s b e in g ch o p p ed .

T h is c a n be done e i t h e r by m e c h a n ic a l c o n ta c t s on th e ch o p p e r

s h a f t , o r by an a u x i l i a r y l i g h t beam bounced o f f th e c h o p p e r .

T h is beam w ould th e n , by way o f some p h o t o c e l l s , s w itc h vacuum

tu b e s o r t r a n s i s t o r s on and o f f to a c c o m p lis h t h e r e c t i f i c a t i o n .

I n g e n e r a l , t h e b a n d w id th : fo r t h i s ty p e o f sy s te m c o u ld b e as

sm a ll a s 1 o r 2 H z, a s com pared to 5 o r 6 Hz w i th a r e l a t i v e l y

s im p le tu n e d a m p l i f i e r , a t a s ig n a l f r e q u e n c y o f 100 H z. A p h a se

s e n s i t i v e d e t e c t o r was t r i e d b r i e f l y , b u t p ro v e d to b e h a rd to

a d ju s t and d id n o t p r o v id e s u f f i c i e n t l y im proved p e rfo rm a n c e to

w a r ra n t i t s u s e . I f t h e s ig n a l l e v e l s i n t h i s e x p e rim e n t were

a n o th e r o r d e r o f m ag n itu d e lo w e r , o r a b e t t e r m agnet a v a i l a b l e ,

t h i s p ro b a b ly w ould n o t b e t r u e .


T h ere i s a t h i r d m ethod o f im p ro v in g th e s ig n a l to n o i s e

r a t i o w hich h a s become im p o r ta n t i n r e c e n t y e a r s . T h is i s th e

te c h n iq u e o f a u t o c o r r e l a t i o n . I n e s s e n c e , th e in co m in g s ig n a l i s

p h a se s h i f t e d and com pared w ith th e u n p h a s e s h i f t e d s i g n a l . I f

th e s ig n a l i s p e r i o d i c , th e s h i f t e d and u n s h i f t e d v e r s io n s w i l l be

c o r r e l a t e d , and th e i n t e g r a l o f th e p ro d u c t o f th e tw o , w h ich i s

23w hat i s m e a su re d , w i l l n o t be z e ro . The n o i s e i s n o t p e r io d i c

and w i l l n o t be c o r r e l a t e d . T h is m ethod was n o t t r i e d , b u t i s

m en tio n ed to i n d i c a t e a n o th e r a v a i l a b l e te c h n iq u e .

The n e c e s s i t y o f haeving a c h o p p e r i n an a - c sy s tem i s

a c t u a l l y an a d v a n ta g e . I f a d -c sy s te m w ere u s e d , a beam s p l i t t e r

w ould be n e c e s s a ry * b u t t h i s m eans t h a t p a r t o f th e beam w ould be

a b so rb e d h e r e , l e a v in g l e s s l i g h t a v a i l a b l e f o r th e e x p e r im e n t .

The c h o p p e r was p la c e d b e f o r e th e sam ple so t h a t th e beam n e e d

n o t p a s s th ro u g h any m a t e r i a l o th e r th a n th e sam p le .

I n c o n s id e r in g th e p h y s ic a l a rra n g e m e n t o f th e sam ple and

r e f e r e n c e beams th e f a c t t h a t th e i n t e n s i t y o f l i g h t r e f l e c t e d

from a m e ta l depends on th e a n g le o f in c id e n c e , w a v e le n g th and

p la n e o f p o l a r i z a t i o n s h o u ld b e c o n s id e r e d . T hus, m ir r o r s

sh o u ld n o t b e p la c e d b e tw e en th e sam ple and th e a n a ly z e r s in c e

th e p la n e o f p o l a r i z a t i o n i s c h a n g in g i n t h i s r e g io n . F o r th e

same r e a s o n , m ir r o r s s h o u ld n o t be p la c e d b e tw e en th e a n a ly z e r

and p h o to tu b e . M ir r o r s c a n be p la c e d i n th e r e f e r e n c e beam

b e c a u s e i t i s n o t a f f e c t e d by th e m a g n e tic f i e l d . I n any c a s e ,

th e m ost s im p le and e le g a n t a rra n g e m e n t i s t h a t o f a l lo w in g th e

sam ple beam to p a s s s t r a i g h t th ro u g h th e sy s tem and h a v in g th e


r e f e r e n c e beam b e n t a ro u n d . Only i n th e c a se o f a u to m a tic o p e r

a t i o n do th e beams have t o t r a v e r s e e q u iv a le n t p a th s .

T here a r e a num ber o f f a c t o r s w hich in f lu e n c e th e s e n s i t i v i t y

o f th e in s t r u m e n t . F i r s t th e p ro b le m o f a n a ly z e r p o s i t i o n w i l l

b e c o n s id e r e d . The i n t e n s i t y o f l i g h t t r a n s m i t t e d by a p o l a r i z e d

and a n a ly z e r o r ie n te d a t an a n g le ^ w i th r e s p e c t to each o th e r

i s g iv e n by

I z A c o s 2© (5 )

T a k in g th e d e r i v a t i v e y i e l d s

- d l - 2A cos © s i n © d© ( 4)

so th e f r a c t i o n a l change i n i n t e n s i t y f o r a change i n a n g le d© i s

2 ta n © d© (5 )

T hus, th e a n a ly z e r p o s i t i o n w hich g iv e s th e m ost s e n s i t i v i t y i s

90 d e g r e e s , 1 . _e., p o l a r i z e r and a n a ly z e r c r o s s e d . H ow ever, a t

t h i s p o i n t z e ro t o t a l amount o f l i g h t i s a v a i l a b l e t o make th e

m easu rem en t. T hus, one sh o u ld u s e th e l a r g e s t © w hich w i l l a llo w

enough l i g h t to p a s s to make th e m easu rem en t. One i s te m p te d to

d e f in e a f i g u r e o f m e r i t i n some f a s h i o n and a t te m p t t o e s t im a te

th e m ost e f f i c i e n t v a lu e o f 9 f o r a g iv e n p h o to tu b e , l i g h t s o u rc e

and a m p l i f i e r , b u t i n p r a c t i c e © c an e a s i l y be d e te rm in e d

e m p i r i c a l l y . H ost o f th e m easu rem en ts i n t h i s s tu d y w ere made

a t a © o f 80 d e g re e s .

The n o is e l e v e l o f th e d e te c t i o n sy s tem i s , o f c o u r s e , q u i te

im p o r ta n t . S e le c te d low n o is e tu b e s w ere u s e d i n th e a m p l i f i e r

and w irew ound o r d e p o s i te d c a rb o n r e s i s t o r s w ere u s e d i n th e in p u t

s t a g e s . I n p r i n c i p l e , n o is e c an be re d u c e d by u s in g a c a sc o d e


26

( u s in g one tu b e as t h e lo a d f o r a n o th e r ) c o n f i g u r a t io n f o r th e i n

p u t s t a g e , b u t some p r e v io u s work by th e a u th o r i n d i c a t e d t h a t

th e a d v a n ta g e s would p ro b a b ly be m a rg in a l .

S t r a y l i g h t e n t e r in g th e p h o t o m u l t i p l i e r h o u s in g c a n c o n t r i

b u te c o n s id e r a b ly to th e g e n e ra l n o is e l e v e l . F o r t h i s r e a s o n

th e l i g h t p a th s l e a d in g d i r e c t l y i n t o th e h o u s in g sh o u ld b e c o v e r

ed w ith b la c k p a p e r and th e h o u s in g p a in te d f l a t b la c k i n s i d e .

The m ir r o r s i n th e r e f e r e n c e beam p a th and th e o p t i c a l com ponents

i n th e sam ple beam p a th a c t a s c o l l i m a t o r s , so t h a t s h i e l d i n g o f

th e e n t i r e l i g h t p a th s i s n o t n e c e s s a r y . N o ise a l s o a r i s e s i n

th e p h o to m u l t i p l i e r i t s e l f due to random th e rm io n ic e m is s io n .

T h is c a n be re d u c e d c o n s id e r a b ly by c o o l in g th e p h o t o m u l t i p l i e r ,

b u t was n o t a t te m p te d .

F a c to r s w hich c a n a f f e c t b o th th e s e n s i t i v i t y and th e a c c u r

acy a r e th e r e l a t e d ones o f sam ple c e l l l e n g t h and c o n c e n t r a t io n .

The F a ra d a y e f f e c t i s p r o p o r t io n a l to b o th c e l l l e n g th and con

c e n t r a t i o n . H ere one i s f a c e d a g a in w i th t h e s i t u a t i o n t h a t

i n c r e a s e d r o t a t i o n m eans d e c re a s e d l i g h t . H ow ever, t h e r e i s an

a d d i t i o n a l f a c t o r . M ost s u b s ta n c e s w i l l b e m easu red i n s o lu t i o n

and th e r o t a t i o n due to th e s o l u t e i s a l l t h a t i s r e a l l y o f i n

t e r e s t ( u n l e s s s o l u t e — s o lv e n t i n t e r a c t i o n s a r e b e in g s t u d i e d ) .

I t c an be seen , t h a t a s th e c o n c e n t 'r a 't io n becom es h ig h e r , th e p e r

c e n ta g e o f th e t o t a l r o t a t i o n w hich i s due to th e s o l u t e becom es

l a r g e r . S o , i f th e c e l l le n g th i s s h o r te n e d and th e c o n c e n t r a t io n

in c r e a s e d su c h t h a t th e r o t a t i o n and a b s o r p t io n rem a in th e same^

a l a r g e r e f f e c t w i l l be o b s e rv e d . T h is i n e f f e c t i n c r e a s e s th e


s e n s i t i v i t y . 1 .0 mm, 1 .0 cm, and 5 .0 cm c e l l s w ere a v a i l a b l e . The

1 .0 cm c e l l was dam aged, a l lo w in g r u s t t o fo rm . S in c e c le a n in g

th e c e l l w ould n o t p r e v e n t r u s t from r e f o r m in g , t h i s c e l l was

n o t u s e d .

The p r e s e n c e o f n on -m onoch rom atic l i g h t c a n in f lu e n c e th e

a c c u ra c y o f t h e r e s u l t s . I f s e v e r a l w a v e le n g th s a r e p r e s e n t ,

t h e m easu red r o t a t i o n w i l l be some s o r t o f a sum o f th e r o t a t i o n s

f o r th e i n d iv i d u a l w a v e le n g th s . What i s s u r p r i s i n g i s th e l a r g e

8e f f e c t a s m a ll amount o f s t r a y l i g h t c a n h a v e . S hashoua r e

p o r te d t h a t s t r a y l i g h t i n th e am ount o f 0 .1 t o 1 .0 p e r c e n t can

c a u se r e p r o d u c ib le e r r o r s o f 10 t o 100 p e r c e n t . F o r t h i s r e a s o n ,

c o n s id e r a b le p r e c a u t io n s w ere ta k e n t o i n s u r e r e a s o n a b ly p u re

l i g h t .

S in c e th e u n i t i s in te n d e d t o o p e r a te to 3000 A, a few

comm ents on o p t i c a l m a t e r i a l s and s e l e c t i o n o f p h o to tu b e s and

l i g h t s o u r c e s a r e p a r t i c u l a r l y n e c e s s a r y .

G la s s c a n n o t b e u s e d much b e lo w 4000 A, A l l th e co m m erc ia l

eq u ip m en t u s e d f o r t h i s in s t r u m e n t c o n ta in s q u a r t z o r fu se d

s i l i c a ’ o p t i c s ; th e t r a n s m is s io n o f g l a s s i s n o t a p ro b le m .

S in c e fu s e d s i l i c a i s an am orph ic v e r s io n o f q u a r t z w ith th e

a d v a n ta g e t h a t i t i s n o t d o u b ly r e f r a c t i n g , i t i s u s e d f o r

c e l l windows and some o th e r co m p o n en ts .

M easu rem en ts o f t h i s ty p e r e q u i r e a n e a r ly c o n tin u o u s l i g h t

s o u r c e . A x enon com pact a r c c a n be u s e d b e c a u s e i t i s a h ig h

i n t e n s i t y c o n tin u o u s l i g h t s o u r c e . A num ber o f o t h e r s o u rc e s


28

m ig h t p e rh a p s h e b e t t e r , such a s a h ig h p r e s s u r e h y d ro g en o r

m ercu ry lam p . A z irc o n iu m p o i n t s o u rc e can. be u se d f o r work i n

t h e v i s i b l e p o r t i o n o f th e sp e c tru m .

An e x a m in a tio n o f th e s p e c t r a l re s p o n s e c u rv e s o f a v a i l a b l e

p h o t o m u l t i p l i e r s p ro d u c e d s e v e r a l w hich would b e u s e f u l . The

RCA 7200 i s p ro b a b ly one o f th e b e s t , b u t h a s th e d is a d v a n ta g e o f

h ig h c o s t . The RCA 1P28 u se d i s a s ta n d a r d UV p h o to m u l t i p l i e r

tu b e , commonly a v a i l a b l e a t low c o s t .


CHAPTER V

INSTRUMENTAL DETAILS

The m ethod c h o se n , a s i n d i c a t e d e a r l i e r , i s b a se d on a d o u b le

beam a p p ro a c h . The g e n e ra l a rra n g e m e n t i s i n d i c a t e d i n F ig u re 8 ,

and p h o to g ra p h s i n F ig u re 9 . The d e s c r i p t i o n o f th e a p p a ra tu s

w i l l p ro c e e d from l e f t t o r i g h t i n F ig u re 8 .

L ig h t S o u rce

Two p r im a ry l i g h t s o u rc e s w ere t r i e d — a 1 5 0 -w a tt xenon

com pact a rc and a 5 0 0 -w a tt z irc o n iu m p o in t s o u r c e . A d -c c a rb o n

a r e was t r i e d b r i e f l y , b u t i t p ro v ed to be much to o u n s ta b l e f o r

u s e i n t h i s e x p e r im e n t.

The xenon com pact a r e i s th e s o u rc e u s e d f o r th e m a jo r i ty o f

th e work r e p o r t e d h e r e . The lam p u s e d i s a H an o v ia 901C-1 w hich

o p e r a te s on 8 .5 amps d - c . The e x i s t i n g R udolph 914 pow er su p p ly

( d e s ig n e d f o r a -c o p e r a t i o n .o f th e 510C-1 lam p) h a s b e e n m o d if ie d

to a llo w d -c o p e r a t io n . The o r i g i n a l s t a r t i n g c i r c u i t h a s b e e n

r e t a i n e d , and th e lamp c o n n e c t io n s b ro u g h t o u t on th e s id e o f th e

c a s e to a llo w c o n n e c t io n to a d -c m o to r g e n e r a to r s e t . The

m o d if ie d c i r c u i t d iag ram i s shown i n A ppendix A. The lamp h ous

in g h as b e e n u se d w ith o u t c h a n g e . An im p o r ta n t p o in t to c o n s id e r

i n a l i g n in g th e lamp w ith th e r e s t o f th e equ ipm en t i s th e f a c t

t h a t m ost o f th e l i g h t o u tp u t i s c e n te r e d on th e c a th o d e . F o r

t h i s r e a s o n , th e c e n t e r o f th e a r c sh o u ld n o t b e a l ig n e d on th e

e n tr a n c e s l i t o f th e sy s te m . The g e n e ra l a l ig n m e n t p ro c e d u re i s

29



XenonLamp

BLOCK DIAGRAM OF INSTRUMENT AS CONSTRUCTED

Z------------------------------ ^

P o la r i z e r -

0- — 0 -

Durrum J a r r e l l - A s hM onochromator M onochromator

---------------

FIGURE 8

------------- d H

Chopper and

M otor Magnet

-Photom ult ip H e r H ousing

CathodeF o llo w e r

TunedA m p lif ie r

O s c illo s c o p e M eter

uoo

EQUIPMENT PHOTOGRAPHS

A: Mono chrom at o rs

7 1 T ^

B: Magnet and P o la r im e te r

FIGURE 9


o u t l i n e d i n A ppendix B . The z irc o n iu m p o in t s o u rc e was u se d f o r

some p r e l im in a r y m easu rem en ts b e f o r e th e xenon lam p a r r i v e d . The

z irc o n iu m lam p i s an e x c e l l e n t s o u rc e o f c o n tin u o u s r a d i a t i o n

down to a b o u t 4000 A, b u t i s n o t a t a l l s a t i s f a c t o r y be low t h a t .

C om parison s p e c t r a o f th e two l i g h t s o u rc e s a r e shown i n

F ig u re 1 0 .

M onochrom ators

The tw o m onochrom ators u s e d a r e a J a r r e l l - A s h 0 .2 5 m e te r

E b e r t and a Durrum 0 .3 0 m e te r C z e rn y -T u rn e r . The J a r r e l l - A s h

in s t r u m e n t em ploys two g r a t i n g s , one b la z e d f o r maximum e f f i c i e n c y

a t 6000 A, th e o t h e r a t 3000 A. I t h a s p l u g - i n s l i t s a v a i l a b l e

i n v a r io u s f ix e d w id th s , o f w h ich th e 100 m ic ro n 3 iz e was on

h a n d . W aveleng th r e a d o u t i s d i g i t a l .

The Durrum in s t r u m e n t u s e s a g r a t i n g w i th a 5000 A b la z e to

c o v e r th e r e g io n from 10000A to 3300 A, and a fu s e d s i l i c a p r ism

i n a L i t t r o w m o u n tin g f o r th e r e g io n from 1800 A to 3300 A. A

s e r i e s o f h ig h p a s s f i l t e r s a re in c o r p o r a te d i n t o th e in s t r u m e n t ,

a l lo w in g some o f t h e s t r a y l i g h t to be b lo c k e d . C o n tin u o u sly

a d ju s t a b le s l i t s a r e em ployed and w a v e len g th re a d o u t i s on a

s c r o l l ty p e s c a l e .

As d is c u s s e d p r e v io u s ly , th e r e d u c t io n o f s t r a y l i g h t l e v e l s

i s o f some im p o r ta n c e i n F a rad a y e f f e c t s t u d i e s . The amount o f

s t r a y l i g h t p r e s e n t i n each m onochrom ator was d e te rm in e d by ob

t a i n i n g a sp ec tru m o f th e l i g h t com ing o u t o f th e u n i t . A H i lg e r

medium d i s p e r s io n q u a r t z s p e c t r o g ra p h (C ornu m ounting) was u se d


33


w ith Kodak SA-3 p l a t e s f o r t h i s p u rp o s e . The J a r r e l l - A s h u n i t

was a d ju s t e d a c c o r d in g to i n s t r u c t i o n s s u p p l i e d w i th th e

in s t r u m e n t . S in c e a d ju s tm e n t i n s t r u c t i o n s w ere n o t a v a i l a b l e

f o r th e Durrum u n i t , i t was t e s t e d as. i s . The r e s u l t s a r e i n

d i c a t e d i n F ig u re 1 1 . C le a r ly , n e i t h e r u n i t by i t s e l f w ould be

s a t i s f a c t o r y . T h e r e f o r e i t was d e c id e d to u s e th e two u n i t s

t o g e t h e r so t h a t th e y w ould a c t a s a d o u b le m onoch rom ato r.

The: b e s t im a g in g i s o b ta in e d w ith t h e l i g h t s o u rc e fo c u s e d

on th e e n t r a n c e s l i t o f th e Durrum in s t r u m e n t and o u tp u t l i g h t o f

t h e Durrum in s t r u m e n t f o c u s e d w ith a q u a r t z l e n s on th e J a r r e l l -

Ash m o n och rom ato r. The J a r r e l l - A s h m onochrom ator i s u s e d w ith

o u t s l i t s and i n e f f e c t a c t s a s a tu n e a b le f i l t e r . I n o p e r a t io n

th e w a v e le n g th i s s e t on th e Durrum in s t r u m e n t and th e J a r r e l l -

Ash tu n e d f o r maximum t r a n s m is s io n , a s i n d i c a t e d by th e p h o to

m u l t i p l i e r o u tp u t v o l t a g e .

P o la r im e te r and Sam ple C e l ls

The p o la r im e te r u s e d i s a R udolph M odel 80 w i th q u a r tz

o p t i c s . The s c a l e c an b e r e a d d i r e c t l y to 0 .0 0 1 d e g re e o f a r c .

The o n ly m o d i f ic a t io n s a r e th e a d d i t i o n o f a mask t o th e e x i t

s id e o f th e a n a ly z e r t o b lo c k o f f t h e d e v ia te d r a y from th e q u a r t z

c r y s t a l and th e a d d i t i o n o f s u p p o r t s f o r th e R e fe re n c e beam m ir

r o r s , a s shown i n th e p h o to g ra p h , F ig u re 9 . T hese s u p p o r t s a r e

f a s t e n e d by th e sc re w s d e s ig n e d t o s e c u r e th e sam ple c e l l h o ld e r

i n ORD w ork .


MONOCHROMATOR SPECTRA

FIGURE 11

Top g roup : Durrum O .3O M C z e rn y -T u rn e r•Bottom group : J a r r e l l - A s h 0 .2 5 M E b e r t .W avelength s e t t in g s ( f r o m to p t o b o tto m ):

2500 A, 3000 A, 3500 A, 5000 A.

R eproduced with permission of the copyright owner. Further reproduction prohibited without permission

The sam ple c e l l s a r e s ta n d a r d R udolph ORD c e l l s o f l e n g th

0 .1 , 1 .0 , 5 .0 , and 10 cm. The 0 .1 and 1 .0 cm c e l l s a r e o f m e ta l

c o n s t r u c t i o n and a r e s l i g h t l y m a g n e tic . The o th e r c e l l s a r e

g l a s s w i th th re a d e d m e ta l end r i n g s f o r th e a tta c h m e n t o f end

p l a t e s . The end p l a t e s i n a l l c a s e s a r e h e ld on by p r e s s u r e

from a sc re w c a p . B o th g la s s and fu s e d s i l i c a e n d p la te s a r e

a v a i l a b l e . A t 5000 A, th e f u s e d s i l i c a e n d p la te s show r o t a t i o n s

o f a b o u t 0 .5 d e g re e .

M agnet and Pow er S upp ly

The m agnet u se d was c o n s t r u c te d a t The U pjohn Company. I t

c o n s i s t s o f tw o w in d in g s o f #13 c o p p e r w ire w ith 1625 tu r n s i n

e a c h w in d in g . B etw een th e w in d in g s and on each end i s l o c a t e d a

p an cak e o f c o p p e r tu b in g f o r c o o l in g p u rp o s e s .

The c e n te r tu b e i s o f th e p ro p e r d ia m e te r to a c c e p t th e

R udo lph sam ple c e l l s . A t h i n ru b b e r w ash e r i s a t t a c h e d to one

p o le p ie c e so t h a t th e c e l l s a r e h e ld t i g h t l y i n p l a c e .

The o r d e r o f m agn itude o f th e f i e l d p ro d u ced was m easu red

u s in g th e r o t a t i o n o f 5000 A l i g h t by w a te r . The f i e l d was a b o u t

8000 g a u ss w ith th e 1 .0 cm c e l l and a c u r r e n t o f 5 a m p e res . No

a tte m p t was made to o b t a in a c c u r a te v a lu e s o f th e f i e l d ; t h e r e -

“ f o r e , th e r o t a t i o n s q u o te d i n t h i s t h e s i s a r e n o t to be c o n s id e re d

a b s o lu te r o t a t i o n s .

T herm ocup les a r e lo c a te d a t u n s p e c i f ie d p o s i t i o n s i n th e

w in d in g s . At 5 am p e res , a l l te m p e ra tu re s rem a in ed 20 d e g re e s

c e n t i g r a d e , o r l e s s , above a m b ie n t.


The m agnet i s pow ered "by a S o re n se n SR-2 e l e c t r o n i c a l l y

r e g u la te d s u p p ly , r a t e d a t 300 v o l t s and 10 a m p e res . The su p p ly

i s n o t c u r r e n t r e g u l a t e d , h u t th e m agnet i s n o t on lo n g enough a t

any one tim e t o c a u se la c k o f c u r r e n t r e g u l a t i o n to be a p ro b le m .

E l e c t r o n i c s

The p h o t o m u l t i p l i e r tu b e u s e d i s an RCA I P 28. The tu b e i s

hou sed i n a .b u i l t - u p alum inum box p a in t e d f l a t b la c k i n s i d e and

e l e c t r i c a l l y g ro u n d ed . The box i s a t t a c h e d t o th e p o l a r im e te r

by a s m a ll tu b e i n s e r t e d i n to th e h o le d e s ig n a te d f o r a t e l e s c o p e .

The p h o to m u l t i p l i e r pow er su p p ly i s a f u l l wave c i r c u i t w ith g a s -

tu b e r e g u l a t i o n .

The a m p l i f i e r i s a s t r a ig h t f o r w a r d c i r c u i t em ploy ing 3 tu n e d

s t a g e s . T u n in g i s a c c o m p lish e d by m eans o f L-C c i r c u i t s i n th e

p l a t e o f e a ch s ta g e . The r e c t i f i e r and m e te r c i r c u i t s a r e a d a p ta

t i o n s from th e H ew le t P a c k a rd 400AB a -c vacuum tu b e v o l tm e te r .

The o u tp u t o f th e a m p l i f i e r d r iv e s a 1 mA m e te r i n p a r a l l e l w ith

1000 ja f . The tim e c o n s ta n t i s s u f f i c i e n t l y lo n g to damp o u t some

o f th e n o i s e , b u t s h o r t enough t h a t th e b a la n c e p o in t c an be e a s i

l y l o c a t e d .

An o s c i l lo s c o p e i s c o n n e c te d ahead o f th e tu n e d s ta g e s to

a id i n a d ju s tm e n t and a lig n m e n t o f th e o p t i c a l sy s te m . F ig u re 12

shows t y p i c a l w aveform s o b ta in e d from th e p h o t o m u l t i p l i e r tu b e .


PHOTOMULTIPLIER OUTPUT SIGNAL

FIGURE 12

Tops Sam ple Learn, s i g n a l .B ottom s R e fe re n c e beam s i g n a l . C e n te rs Sum o f sam p le and r e f e r e n c e

beam s i g n a l s .


M is c e lla n e o u s O p t ic a l Com ponents

F r o n t s u r f a c e a lu m in iz e d m i r r o r s , o b ta in e d from th e Edmund

S c i e n t i f i c Company, a r e u se d to bend th e r e f e r e n c e beam.

The c h o p p e r i s c o n s t r u c te d o f y e llo w b r a s s and h a s m ir r o r s

g lu e d t o i t s se g m e n ts . The two m ir r o r s a r e o f e q u a l m ass , b u t

t h e c h o p p e r i s n o t d y n a m ic a lly b a la n c e d . The c h o p p e r i s d r iv e n

by a sy n c h ro n o u s p h o n o g rap h m o to r .

A p ie c e o f p l a s t i c P o l a r o i d m a t e r i a l i s u s e d a s th e r e f e r

ence beam a t t e n u a t o r . T h is i s a d e q u a te e x c e p t below 3000 A

w here th e p l a s t i c a b s o rb s t h e i n c i d e n t l i g h t a lm o s t c o m p le te ly .


CHAPTER V I

INSTRUMENT PERFORMANCE

An a t te m p t w i l l now be made t o o u t l i n e th e p e rfo rm a n c e o f

th e f i n a l v e r s i o n o f th e in s t r u m e n t .

The f i r s t i te m to be c o n s id e re d i s a e ro p o i n t s t a b i l i t y .

T h is can be o f some im p o r ta n c e b e c a u se o f th e f i n i t e t im e ( a b o u t

30 seco n d s) in v o lv e d i n t a k in g m ea su rem e n ts . F l u c tu a t i o n s o f 0 .1

d e g re e o v e r th e p e r io d o f a r e a d in g w ere found o n ly o c c a s i o n a l l y .

I n f a c t , m easu rem en ts show ing a z e ro p o i n t s h i f t o f 0 .1 d e g re e

w ere u s u a l l y d i s c a r d e d b e c a u s e s h i f t s o f 0 .0 5 d e g re e o r l e s s w ere

much more common. I n many c a s e s , no d e t e c t a b l e s h i f t was n o te d .

I n c a s e s w here th e z e ro d id s h i f t , th e mean o f th e two z e ro r e a d

in g s was u se d a s th e f i n a l z e ro v a lu e .

F ig u re 13 i s a c h a r t show ing th e o u tp u t s i g n a l o f th e s y s te m .

The p u l s e s r e p r e s e n t r o t a t i o n s o f 0 .5 d e g re e and w ere o b ta in e d by

r a t a t i n g th e a n a ly z e r 0 .5 d e g r e e . The n o i s e l e v e l i s a b o u t 0 .0 1 5

d e g re e .

A c h eck was made t o d e te rm in e th e e f f e c t o f r e v e r s in g th e

d i r e c t i o n o f th e m ag n e tic f i e l d . A t 3000 A, w ith w a te r i n th e

1 .0 mm c e l l , th e f o l lo w in g r o t a t i o n m easu rem en ts w ere mades

1 . R o ta t io n o b ta in e d w ith f i e l d d i r e c t i o n su c h t h a t w a te r r o t a t e s th e p la n e o f p o l a r i z a t i o n c lo c k w is e ( p o s i t i v e r o t a t i o n ) : 1 .9 9 d e g r e e s .

2 . R o ta t io n o b ta in e d w ith f i e l d r e v e r s e d ( n e g a t iv e r o t a t i o n )2 .0 0 d e g re e s .

40


41

Phgo


FIGU

RE

13

42

3 . One h a l f th e r o t a t i o n o b ta in e d by a llo w in g th e z e ro c o n d i t io n to be f i e l d on ( p o s i t i v e d i r e c t i o n ) , and th e n r e v e r s in g th e d i r e c t i o n o f th e f i e l d : 1 .9 9 d e g r e e s .

Each num ber i s th e mean o f th r e e t r i a l s and th e s p re a d i n v a lu e s

f o r e a c h s e t o f th r e e t r i a l s i s 0 .0 2 d e g re e . The o n ly a d v a n ta g e

i n r e v e r s i n g th e f i e l d w ould b e to o b t a i n an e f f e c t tw ic e a s l a r g e

a s n o rm a l.

The n e x t f a c t o r to b e d i s c u s s e d i s th e e f f e c t o f m aking

m easu rem en ts w ith th e a n a ly z e r i n d i f f e r e n t q u a d r a n ts . The

f o l lo w in g was o b se rv e d :

W av elen g th Q u ad ran t R o ta t io n o f W ater i n 1 mm C e ll

3000 A 1 1 .9 72 1 .9 9 mean 1 .9 93 2.014 1 .9 9

5000 A 1 0 .6 82 0 .6 1 mean 0 .6 53 0 .6 94 0 .6 3

T h ere a p p e a r s to b e a s i g n i f i c a n t v a r i a t i o n a t 5000 A and a s m a ll

v a r i a t i o n a t 3000 A. S in c e th e same q u a d ra n t i s u se d f o r a l l

m e a su re m e n ts , t h i s e f f e c t s h o u ld c a n c e l when th e s o lv e n t r o t a t i o n

i s s u b t r a c t e d from th e t o t a l r o t a t i o n . T h e r e f o r e , th e r e s u l t s a re

r e p o r t e d w i th o u t t h i s c o r r e c t i o n .

The a n a ly z e r s c a l e h a s v e r n i e r s on b o th o f i t s s id e s and a t

th e no rm al o p e r a t in g p o s i t i o n o f 10 d e g r e e s , a c o r r e c t i o n o f a b o u t

0 .0 0 8 d e g re e was fo u n d t o be n e c e s s a r y . T h is I s a l s o n e g le c te d

i n r e p o r t i n g th e r e s u l t s , s in c e i t i s c o n s ta n t f o r b o th s o lv e n t

and s o l u t e . The q u a d ra n t d a ta ab o v e , how ever, in c lu d e s t h i s

c o r r e c t i o n .


43

A lth o u g h n o t e s p e c i a l l y im p o r ta n t , th e v a r i a t i o n o f

r o t a t i o n w ith m agnet c u r r e n t was i n v e s t i g a t e d . The n e a r ly

l i n e a r r e s u l t i s shown i n F ig u re 1 4 . A ll r e a d in g s d u r in g th e

a c tu a l e x p e r im e n t w ere ta k e n a t a c o n s ta n t 5 am p eres .

The c e l l windows can exert a profound influence on the

observed rotation s. The s i l i c a endplates used in the present

work had a p p a r a n t ly b e e n s t r a i n e d , b e c a u s e r o t a t i n g th e c e l l

produced variations in rotation of up to 0 ,1 degree. Also,

changing the pressure on the endplates caused s ig n ifica n t24ch a n g es i n t h e r o t a t i o n . K in g r o t a t e d a c o v e r s l i p sm eared

w ith o i l from h i s f i n g e r s and o b se rv e d a p eak t o p eak v a r i a t i o n i n

b a la n c e p o i n t o f a b o u t 0 .0 3 d e g re e . F o r th e s e r e a s o n s some

a t te m p t was made to s t a n d a r d i z e th e m ethod o f a s s e m b lin g th e c e l l .

The c e l l was f i l l e d by a t t a c h i n g one e n d p la t e , p l a c i n g 3 d ro p s

o f th e s o l u t i o n to b e t e s t e d i n th e c e l l * and d ro p p in g th e o th e r

e n d p la te i n t o p l a c e . The e h d p la te s w ere h a n d le d o n ly by t h e i r

e d g e s . The sc re w c a p s and th e body o f t h e c e l l w ere s c r a tc h e d to

a llo w r e t u r n i n g to a p p ro x im a te ly th e same p r e s s u r e e a c h t im e .

The windows had one edge ground s lig h tly ; th is edge was always

placed with the same orientation in the c e l l . The c e l l was

placed in the polarimeter with the scratch marks facing up.

Several water curves were run to check the reproducib ility .

The values of rotation at 5000, 4000, and 3000 A reproduced to

within 0.03 degree in t r ia ls made three d ifferen t days. The

points at 5000 , 4000, and 3000 A are each the mean of none measure

ments. The standard deviation of the mean in each case i s about


ROTATION VERSUS MAGNET CURRENT

2 -5 '

wCDCD

b£)aflo

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1-5^ 5 6 7

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FIGURE Tit-


0 .0 1 d e g re e . The in te r m e d ia t e p o i n t s a r e e a c h th e mean o f t h r e e

m ea su rem e n ts . A c u rv e was f i t t e d to a l l t h e p o i n t s by h a n d .

The s t a t i s t i c a l e r r o r s i n th e w a te r c u rv e a r e u s u a l l y ta k e n

to b e on th e o r d e r o f 0 .0 2 d e g re e . T hus, by th e t im e th e w a te r

c u rv e i s s u b t r a c te d from th e s o lu t i o n c u rv e , th e e r r o r i s a b o u t

0 .0 5 d e g re e *

F ig u re 15 shows th e f i n a l w a te r c u rv e and p o i n t s . A lo g -

lo g p lo t- , p r e s e n te d i n F ig u re 1 6 , was a l s o made o f t h e s e d a t a .

A p p a re n tly , o v e r th e r e g io n o f i n t e r e s t , a s i n g l e te rm d i s

p e r s i o n e q u a t io n w i l l v e ry n e a r ly f i t th e c u rv e . The ex p o n e n t

i s a b o u t - 2 .1 8 , t h a t i s , th e r o t a t i o n i s p r o p o r t i o n a l to tTg.ig .


Rot

atio

n,

Deg

rees

FARADAY ROTATION OF WATER

2 . a .

4500IjOOO W avelen gth , A

3000 3500 5000 5500

FIGURE 15


4 .0

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L0G-L0G PLOT OP THE FARADAY ROTATION OP WATER

2.0 -

1.0

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034)

£ 0.76Do 0.6

£° 0 .5$■po« 0 .4

0 -3 - i -----------1........ ~i--3 4 5W avelength , 1000

T*8

T9 10

FIGURE 16


CHAPTER V I I

DATA

The compounds t e s t e d w ere o b ta in e d from th e C h em is try

D ep artm en t a t W e ste rn M ic h ig a n U n i v e r s i ty . They w ere a l l r e a g e n t

g r a d e , b u t o th e r w is e no s p e c i a l p r e c a u t io n s w ere ta k e n to i n s u r e

p u r i t y . D i s t i l l e d w a te r was u se d i n m ost c a s e s as th e s o lv e n t .

I n g e n e r a l , b e c a u s e th e r o t a t i o n o f th e s o l u t e i s w hat i s o f

i n t e r e s t th e e f f e c t o f th e s o lv e n t m ust somehow b e s u b t r a c te d

o u t . S h ash o u a a c c o m p lish e d t h i s by u s in g two sam ple c e l l s and

two m a g n e ts . The s o l u t i o n to b e m easu red was c o n ta in e d i n one

c e l l and m agnet and th e s o lv e n t i n th e o th e r c e l l and m ag n e t.

The c u r r e n t i n th e seco n d m agnet w as, how ev er, r e v e r s e d , so t h a t

r o t a t i o n due to th e s o lv e n t a lo n e c a n c e l le d t h a t due to th e

s o lv e n t i n th e s o l u t i o n . S in c e t h i s a p p ro a c h was n o t p r a c t i c a l

i n th e p r e s e n t c a s e , th e s o lu t i o n and s o lv e n t r o t a t i o n s w ere

m easured s e p a r a t e l y and s o lv e n t r o t a t i o n s w ere s u b t r a c te d from

th e s o l u t i o n r o t a t i o n s t o o b ta in th e s o lu t e r o t a t i o n s . To be

p e r f e c t l y c o r r e c t , one s h o u ld ta k e i n t o a c c o u n t th e d i f f e r e n c e s

i n d e n s i ty b e tw een th e s o l u t i o n and s o lv e n t , a s in d ic a te d by

S h ash o u a . As m en tio n e d i n C h a p te r VT, th e s e c o r r e c t i o n s have

b e e n n e g le c te d w ith t h e u n d e r s ta n d in g t h a t a b s o lu t e r o t a t i o n s

a r e n o t b e in g p r e s e n te d i n t h i s p a p e r (o n e m ust s t i l l b e c a r e f u l

a b o u t c o m p arin g compounds t e s t e d i n d i f f e r e n t c o n c e n t r a t i o n s ) .

As i n d i c a t e d e a r l i e r , no p a r t i c u l a r r u l e s g overned th e c h o ic e

o f com pounds. N ic k e l s u l f a t e and f e r r i c c h lo r i d e w ere c h o se n so

48


t h a t some o f t h e r e s u l t s c o u ld be com pared t o p r e v io u s w ork .

P o ta s s iu m io d id e was c h o se n t o r e p r e s e n t th e in o r g a n ic d ia m a g n e tic

compounds b e c a u s e i t a b s o rb s i n a c o n v e n ie n t r a n g e , a b o u t 3200 A.

C u p ric s u l f a t e was c h o se n to o b ta in an exam ple o f a n o th e r i r o n

g roup io n .

Comments on th e i n d iv i d u a l io n s f o l lo w .

P o ta s s iu m I o d id e

A t e n p e r c e n t s o lu t io n , g iv e s b e s t r e s u l t s . The r o t a t i o n

c u rv e i s shown i n F ig u r e 1 7 . T h is a p p e a rs t o be a ty p e I s p e c t

rum w ith p e a k s u n e q u a l i n a m p litu d e , b u t c o u ld be i n t e r p r e t e d as

a ty p e I I s p e c tru m , s in c e r e a d in g s be low 3000 A w ere n o t p o s s i b l e .

The a b s o r p t io n p e a k o c c u rs a t ab o u t t h e w a v e le n g th o f th e lo w e s t

p o i n t on th e r o t a t i o n c u r v e .

C u p ric S u l f a t e

A one p e r c e n t s o l u t i o n g iv e s a t y p i c a l ty p e I I s p e c tru m , as

i n d i c a t e d i n F ig u re 1 8 . T h is s o l u t i o n i s tcro weak to a l lo w an

a b s o r p t io n c u rv e to be made w ith t h i s in s t r u m e n t . N ote t h a t

t h e r e i s a s u g g e s t io n t h a t th e r o t a t i o n i s n e g a t iv e b e lo w th e

a b s o r p t io n and p o s i t i v e above i t , m ore o r l e s s i n ag reem en t

w i th some o f th e r e s u l t s q u o te d i n th e th e o r y s e c t i o n . I f th e

r o t a t i o n i s p r o p o r t i o n a l t o c o n c e n t r a t io n , c o p p e r s u l f a t e e x h ib i t s

c o n s id e r a b ly more a c t i v i t y th a n p o ta s s iu m i o d id e . The n e x t s te p

s h o u ld p ro b a b ly b e th e d e te r m in a t io n o f th e e f f e c t o f c o n c e n t ra

t i o n on th e c u r v e .


FARA

DAY

ROTA

TION

OF

KI

50

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52

F e r r i c C h lo r id e

S hashoua o b ta in e d a ty p e I I sp e c tru m f o r t h i s compound i n

a l c o h o l . S e v e ra l a t te m p ts w ere made to r e p e a t t h i s w ork, f i r s t

w i th w a te r and th e n w ith i s o p r o p y l a lc o h o l . A c o n s id e r a b le

amount o f d i f f i c u l t y was e x p e r ie n c e d w ith c o n ta m in a t io n o f th e

s o l u t i o n s , w hich c a u se d them t o d a rk e n p r o g r e s s iv e l y w i th tim e

( T h is e f f e c t was n o t i c e a b le o v e r a p e r io d o f s e v e r a l h o u r s ) .

P a r t o f th e c a u se was e v e n tu a l ly fo u n d to b e th e r u s t on th e i n

s id e o f th e 1 .0 cm c e l l . T h is was d e te rm in e d from th e f a c t t h a t

a p o r t i o n o f t h e s o l u t i o n , when p la c e d i n th e c e l l f o r a b o u t

f i f t e e n m in u te s would become a lm o s t o p aq u e , and no su c h d i f f i c u l t y

was e x p e r ie n c e d w ith th e g l a s s c e l l s o r th e 1 .0 mm c e l l .

The b e g in n in g o f a ty p e I I sp e c tru m i s o b se rv e d i n a 0 .0 1

p e r c e n t s o l u t i o n i n w a te r w i th th e 1 .0 c e l l add a r e l a t i v e l y

good ty p e I I c u rv e i s o b ta in e d i n a 0 .0 1 p e r c e n t s o l u t i o n o f

i s o p r o p y l a lc o h o l . T h is c u rv e i s , how ever, s h i f t e d i n wave

le n g th a s com pared to th e c u rv e r e p o r t e d by S h ash o u a .

N ic k e l S u l f a t e

S e v e ra l r e l a t i v e l y low p r e c i s i o n ru n s w ere made on L o v in g 's

o r i g i n a l s o l u t i o n s . As shown i n F ig u re 1 9 , weak ty p e I s p e c t r a

a r e o b ta in e d f o r th e 0 .7 5 and 2 .0 fo rm a l s o l u t i o n s ( t h e o th e r s

w ere n o t t r i e d ) . T h is i n a g reem en t w ith h i s r e s u l t s , b u t th e

e f f e c t s s e e n h e re a r e n o t a s s t r o n g .


A f r e s h s o l u t i o n o f one p e r c e n t HiSO^SHgO d id n o t e x h i b i t

an anom alous e f f e c t , a s i n d i c a t e d i n F ig u r e 2 0 . A s l i g h t e f f e c t

may b e o c c u r in g above 4000 A b u t t h i s d rop i n r o t a t i o n i s p ro b

a b ly n o t s i g n i f i c a n t .

As i n d i c a t e d i n F ig u r e 21 , a t e n p e r c e n t s o l u t i o n d id e x h i b i t

a v e ry b ro a d ty p e I s p e c tru m , b u t a d d i t i o n a l ru n s w ould b e n e c e s

s a r y to d e te rm in e w h e th e r o r n o t t h i s e f f e c t r e a l l y e x i s t s . I n

any c a s e , th e s t r o n g e f f e c t n o t i c e d by L o v in g does n o t a p p e a r to

b e p r e s e n t . T here i s a l s o th e p o s s i b i l i t y t h a t th e e f f e c t n o t i c

ed h e re i s due to i n t e r a c t i o n s w i th th e s o lv e n t . I n any c a s e ,

t h i s compound s h o u ld be i n v e s t i g a t e d f u r t h e r .


Rot

atio

n,

Deg

rees

FARADAY ROTATION OF NiSO

TT

2500 3000 3500 A000W avelen gth , A

0 .7 5 F

030002500

W avelength , A

FIGURE 19


Rot

atio

n,

Deg

rees

R

otat

ion

, D

egre

es

55

FARADAY ROTATION OF N iS O ^ H gO

1 <p Aqueous S o lu t io n

- 0 . 1 -

- 0 . 2 J500035003000

W avelength , A

FIGURE 20

v 0 . 2 4.1 0 f Aqueous S o lu t io n

- 0 . 1 -

50003000W avelength , A

FIGURE 21


CHAPTER V I I I

SUMMARY AND CONCLUSIONS

In s t ru m e n t

A d o u b le beam , d i r e c t r e a d in g p o la r im e te r f o r s tu d y o f th e

F a ra d a y e f f e c t was c o n s t r u c te d and t e s t e d . S t a t i s t i c a l f l u c t u a

t i o n s i n th e m easu red r o t a t i o n s amount to a b o u t 0 .0 2 d e g re e w ith

e ig h t o r t e n t r i a l s and a re g e n e r a l ly w i th in 0 .0 3 d e g re e f o r

th r e e t r i a l s . S y s te m a tic e r r o r s , due t o n o n u n ifo rm ity o f co n

s t r u c t i o n o f th e a n a ly z e r and i r r e g u l a r i t i e s i n th e s c a l e amount

to ab o u t th e same le v e l, a b o u t 0 .0 3 d e g re e , b u t h ave b een n e g le c te d

b e c a u se th e c u rv e s r e p o r t e d h e re r e f l e c t th e d i f f e r e n c e s b e tw een

th e s o lu t e and s o lv e n t c u rv e s .

The s e n s i t i v i t y o f th e in s t r u m e n t i s on th e o r d e r o f 0 .0 1

d e g re e .

The e r r o r i n t h i s in s t r u m e n t , w h ile a b o u t an o r d e r o f mag

n i tu d e l a r g e r th a n th e b e s t equ ipm en t r e p o r t e d i n th e l i t e r a t u r e ,

i s s t i l l a c o n s id e r a b le im provem ent o v e r some o f th e p h o to g ra p h ic

m e th o d s . The a b s o r p t io n o f l i g h t by th e sam p le i s n o t s e v e r e i f

a 1 .0 mm p a th le n g th i s u s e d .

The p r im a ry f a c t o r w hich n e e d s to be im proved i s th e m ag n e t.

A c o n s id e r a b ly s t r o n g e r f i e l d w ould b e v e ry d e s i r a b l e and i s i n

f a c t a lm o s t n e c e s s a r y , e s p e c i a l l y w ith th e s h o r t e r c e l l l e n g t h s .

The u s e o f an a l l g l a s s c e l l i s a l s o d e s i r a b l e .

56


C o n v e rs io n o f t h i s sy s te m t o c o m p le te ly a u to m a tic o p e r a t io n

■would h e d e s i r a b l e . T he i n s t a l l a t i o n o f a second J a r r e l l - A s h

m onochrom ato r to r e p l a c e t h e Durrum w ould f a c i l i t a t e t h i s con

s id e r a b ly „ s in c e th e J a r r e l l - A s h u n i t s a r e d e s ig n e d t o be

m ounted to g e a t h e r and eq u ip p e d w ith e l e c t r i c a l l y o p e ra te d

w a v e le n g th d r i v e . The e l e c t r o n i c s would have to be m o d if ie d

som ew hat, s in c e th e p r e s e n t equ ipm en t i s p ro b a b ly n o t p r e c i s e

enough f o r u s e i n a s e rv o sy s te m . O p e r a t io n a l a m p l i f i e r s w i th

f re q u e n c y d e p e n d e n t fe e d b a c k m ig h t be t h e b e s t c h o ic e .

M easurem ents

M easu rem en ts made on s e v e r a l i r o n g roup s a l t s a r e i n

g e n e r a l a g re e m e n t w i th th e e le m e n ta ry m odel p r e s e n te d i n th e

t h e o r y s e c t i o n .

The p r im a ry e x c e p t io n i s n i c k e l s u l f a t e . . The w ork r e p o r t e d

h e re ,, a s w e ll a s t h a t o f S h ash o u a , s u g g e s ts t h a t t h e m agneto

o p t i c a l r o t a t i o n c u rv e s o b ta in e d by L o v in g f o r n i c k e l s u l f a t e

may b e a f u n c t io n o f th e p a r t i c u l a r s o l u t i o n s he u se d .. A tte m p ts

to l o c a t e a v a lu e f o r t h e C u rie -W e iss te m p e ra tu re o f n i c k e l

s u l f a t e i n s ta n d a r d handbooks w ere n o t s u c e s s f u l ; h e n c e , a

s e a r c h o f th e l i t e r a t u r e i s n e c e s s a r y . As m en tio n ed i n C h a p te r I I ,

o n ly a no rm al r o t a t i o n c u rv e m ig h t be o b ta in e d i f th e s o l u t i o n

w ere a t i t s C u rie -W e iss tem p e ra tu re .: a t room te m p e ra tu re s The

s t r o n g e r n i c k e l s u l f a t e s o lu t i o n s d id show th e b e g in n in g s o f an


anom alous r o t a t i o n c u rv e . T h is o b s e r v a t io n p o in t s up th e n e c e s s i t y

o f o b t a in in g more in f o r m a t io n a b o u t th e d ep endence o f th e r o t a t i o n

on th e c o n c e n t r a t io n o f th e s o l u t i o n .

I n v e s t i g a t i o n o f th e te m p e ra tu re dependence o f th e r o t a t i o n

o v e r a ra n g e l a r g e enough t o in c lu d e th e C u rie -W eiss and C u rie

te m p e ra tu re s o f th e compound i n q u e s t io n would b e d e s i r a b l e .

The m ag n e tic p r o p e r t i e s o f th e r a r e e a r t h g roup have been

i n v e s t i g a t e d w ith N u c le a r M ag n etic R esonance te c h n iq u e s , b u t

a p p a re n t ly n o t w ith th e F a ra d a y e f f e c t . Such a s tu d y m ig h t p ro v e

i n t e r e s t i n g and im p o r ta n t .


REFERENCES

1 . F a ra d a y , P h i l . T r a n s . , 136 1 ( 1 8 4 6 ) .

2 . J e n k in s and W h ite , F u n d am en ta ls o f O p t i c s . Hew Y ork:Me G ra w -H ill Book Co, I n c . , 3 r d , e d . , 1957 . C h a p te r 29.

3 . P a r t i n g t o n , J . R . , An A dvanced T r e a t i s e on P h y s ic a l . C h e m is try , V o l. IV . London: Longm ans, G reen and C o ., 1 9 5 3 . P p . x l - 6 8 8 .

4 . K a r ts c h a g in and T sch e tw erik o w a , 2 . P h y s ik . . 3 9 , 886 ( 1 9 2 6 ) .

5 . W ilso n and H u l l . P h y s . R ev. , 2&t> 711 ( 1 9 4 8 ) .

6 . D a v ie s , S c i . J o u r . . 2 , Ho. 1 0 , 62 ( l 9 6 6 ) .

7 . Wood, R. W.., P h y s i c a l O p t i c s . New Y ork : M a c m ill ia n C o ., 3 rd .e d . , 1934 . P . 708..

8 . S h ash o u a , J . H h sa . S o c .., 8 6 , 2109 (1 9 6 4 ) .

9 . Me C a r ta n and B a r r a u l t , J . S c i . I n s t r . , 4 4 , 265 ( 1 9 6 7 ) .

10 . Wood, o p . c i t . , p . 71 1 .

1 1 . L o v in g , "D evelopm ent o f a M ethod f o r M e asu rin g M a g n e to -O p tic a l R o ta to ry D i s p e r s io n ." U n p u b lish e d M a s te r 's t h e s i s , W este rn M ic h ig a n U n i v e r s i t y , K alam azoo, M ic h ig a n , A p r i l 1967 . P . 59*

1 2 . B r i a t , Compt. R end. , 256 , 3440 ( 1 9 6 3 ) .

1 3 . B r i a t , Compt. R end. , 259 , 2408 (1 9 6 4 ) a

1 4 . V o lk e n s te in , e t . a l . , N a tu r e , 209 . 709..

15 .. M o r r is h , The P h y s ic a l P r i n c i p l e s o f M agnetism . New Y ork :Jo h n W iley and s o n s , I n c . , 1965 . P . 6 7 .

1 6 . Low ry, T . M ., O p t i c a l R o ta to ry P ow er. New Y ork : D over p u b l i c a t i o n , I n c . , 1964. P p . x i i i - 483..

1 7 . L ow ry , op . c i t . , p . 198 .

1 8 . Wood, o p . c i t . , C h a p te r 21*

1 9 . S t ro n g , C o n cep ts o f C l a s s i c a l O p t i c s . San F r a n c is c o : W. H. F reem an and Co*, 1 958 . A ppendix D.

59


20 . Low ry, o p . c i t . , p . 217.

21 . L evy , e t . a l , , Rev. S c i . I n s t r ; , 21 693 ( 1 9 5 0 ) .

222 F o r s y th e , e t . a l . , A p p lied O p t i c s , 6 , 699 ( 1 9 6 7 ) .

23 . D i tc h b u rn , R . W ., L i g h t . Mew Y ork : I n t e r s c i e n c e P u b l i s h e r s ,I n c . , 2nd . e d . , (1 9 6 3 ) Pp«

2 4 . K in g , J . S c i . I n s t r . , 4 3 , 924 ( 1 9 6 6 ) .


APPENDIX A

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APPENDIX B

METHOD OF ADJUSTMENT

The o p t i c a l com ponents m ust he a c c u r a te ly a l ig n e d i n o rd e r

t o o b t a i n maximum s e n s i t i v i t y . The f o l lo w in g p ro c e d u re i s u s e d

t o s e t up th e sy s te m .

1 . The m onochrom ator s l i t h e ig h t i s a d ju s te d to b e th e sftme a s t h a t o f th e p o l a r im e te r .

2 . The l i g h t s o u rc e i s fo c u se d on th e Durrum m onochrom ato r1 s e n tr a n c e s l i t .

3 . The J a r r e l l - A s h m onochrom ator i s p la c e d so t h a t i t s e n tr a n c e s l i t l i e s a t t h e p o in t w here l i g h t from th e Durrum e x i t s l i t i s b ro u g h t to a fo c u s by th e q u a r t z l e n s .

4 . The p o la r im e te r i s o r ie n t e d and th e m onochrom ator l e v e l e d t o a l lo w l i g h t to p a s s th ro u g h th e sy s te m and f a l l on t h e p h o t o m u l t i p l i e r tu b e . T h is i s done v i s u a l l y w i th th e p h o to m u l t i p l i e r o f f .

5 . S te p num ber f o u r i s r e p e a te d w ith th e p h o t o m u l t i p l i e r on and th e r e f e r e n c e beam b lo c k e d .

6 . The sam ple beam i s b lo c k e d and th e r e f e r e n c e beam m ir r o r s a r e a d ju s te d f o r th e b e s t p o s s ib l e s q u a re wave a t th e p h o t o m u l t i p l i e r o u tp u t .

7 . The sam ple beam i s u n b lo c k e d and th e m i r r o r s a r e r e a d j u s t ed t o p ro d u c e th e lo w e s t p o s s ib l e b a la n c e s i g n a l .

67


the development and use of a double beam photoelectric

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